Here's an idea, maybe you could make it so every month your supporters get to choose what skin is gonna be added to the full game via a poll. this way when the game is complete everyone will get the skins after 100% completion of the game (all scenes, endings etc), but your supporters who give you money get the choice of what ones they'd like to see in the game for whatever character they've decided upon.
i'm sorry that you have to deal with that though, some people just dont understand that people need money to survive. i really enjoy the game and i can't wait to see what the full game brings, keep up the good work!