Facemelting Solos has actually already added the game to their page in a collection!
I've been digging through the woefully lacking FAQs and help pages, but it seems the only way to add a "collaborator" right now is to make them an admin on the project, which then allows full access to upload, delete, basically do anything to the project. It seems devs have been asking for better (or any) options to fine-tune this for awhile now, but no signs of this to date. :(
I've credited FMS on Youtube, twitter, in-game, and on the page, so for now I think I'd rather keep the admin controls attached to my account, since I'm the core developer. If they ever make that update with more options, I'll definitely come back and revisit this! Something to keep an eye on.