any chance this game gets a port as an apk? I hate using joiplay since it takes up way too much space.
Most do it by seperating the rpa file inside the "game" folder and having the apk install everything else. As long as the file location isn't inside android's data folder and somewhere else like the document folder (which is how most devs are doing it now since android is denying access to data files) it's fairly easy for the users to just move or copy the rpa file into the game folder themselves. Just zip the apk and the rpa files together with maybe a txt document for installation instructions and post it up on itch to download. Although I'm not sure specifically how to do any of that since I've never personally done it myself, the method is there you just might need to ask around a bit.
Setup a server to host the game's files. Then create an APK with just a title screen, this title screen app is just there for the user to receive the game's files from an external server. Then have the app just overwrite its files with those downloaded from the external server. Or you can reference/use RADC. RADC should give you an idea of where to start, or you can use it as is while buggy does what is needed.