Maybe the main character could have some way of doing that and more. I remember that you said that there would be other rooms in the sanctuary well one of those rooms could be a dungeon or like a prison and maybe one of the other characters could be like the warden of said prison. The way the player would place someone in the prison is by swallowing them rather than them just being pulled into the sanctuary because they are accepted in they are forcefully pulled into a specific part of the sanctuary which is the prison. Another room could be connected directly to the idea of cock vore where it leads to a contamination/decontamination area.
1. For a contamination room the character would be a hybrid of some kind and would be able to contaminate anyone pulled into the contamination area because it seems to be that contamination goes through cum and sexual interaction.
2. For a decontamination room the character much like above would be instead of hybrid would be human and would be able to remove the affliction of any character or creature that is not human if they were human to begin with otherwise it will create potentially a hybrid effect.
3. For the dungeon it could also double as a playroom if you will essentially all characters within the dungeon area are used as a way of sexual relief for other people in the sanctuary who are not locked in the dungeon and as a way to induce the idea of loyalty to the player and to the characters in the sanctuary.
4. Anal vore could be used as a direct path to an area similar to the sewers, swamp, caves, a farm like area and the way it would work is the fact that those placed in that area help to supply the player and all others in the sanctuary with food if time still flows similarly no matter where they're at.
5. Another effect with the cock vore is that if they choose not to be decontaminated or contaminated they will be an amplification through assimilation as a result the players stats and come load could be changed to have different effects based on whether it's when they have absorbed or not. The assimilation would not be fatal in any way shape or form and they would not completely vanish what I believe what happened is they would then be forced into the milking room which would essentially equate to the players prostate area and essentially they would be milked continually for their cum any player could interchange what their balls are loaded with as they see fit based on the interaction and if you want to leave the character the same or change them without having to be a completely different creature or some sort of hybrid.
6. An idea I just had is that there could also be what I have come to the term of cock fucking and essentially it's like the process of sounding but with somebody else's dick going down your dick and this could be a process that could happen with characters with a larger cock size or smaller cock size then the player and the player wants to have some changes rather than it always being up the ass or swallowed for the conversion to begin maybe the player gets their balls loaded with another creatures loaded.
7. Another idea I had was the concept of the almost impregnation that comes with the slime maybe there is a way that the character could become impregnated with a similar entity or creature through the cock and maybe this is what leads the character to be able to cock vore.
8. Another idea for all of this is that the player can set up situational events for characters that will not and cannot be in the sanctuary. A demonstration of this is the man at the mechanical room with the dog creature for instance forcefully stripping the man of his ass covering gets the dog to mount him and you could join in possibly and maybe as a result rather than getting the man you get the dog creature on your side and add him to the sanctuary or potentially you could add both as a result of doing his quest and getting him fucked by the dog creature.
9. Hopefully the final idea for this at the moment your thoughts on mpreg and based on the idea with the slime and Rohan and potentially what you have planned for the stone golem eggs you seem to be receptive of it. A thought I had is that the player could also become impregnated with non-egg laying creatures and the way this would work is near the bladder through the prostate the player would have a womb of some type The reason I say through the prostate is because the prostate would work much like the cervix keeping me baby in until the player gives birth. I do believe that the character would take the same amount of time as with the slime or the stone golem eggs potentially as to not inconvenience the play of the rest of the game. Another thing that could happen is that while the player is pregnant with an actual baby the creatures that the player may interact with and had sex with maybe able to impregnate the player again while they are still pregnant or potentially impregnate the baby and convert the baby into a hybrid for a tribrid even. The baby could be automatically added to the sanctuary as a nondescript unless you so choose creature that could convert the player into a chimera or hybrid of it for easy access two different conversions.
P.S. sorry this one is so long I just kept having ideas pop into my head that I wanted to suggest and that is all these are are suggestions you are still the Creator and so far you've been creating something amazing despite the fact it's just you you have no help and it's already this amazing that people want to try and help in any way they can.