How about, for every company that 'skins' GFY, you add that to a list of themes for the board and let posters choose the skin that they want to use regularly
Its an added bonus for those companies that have paid you guys money as they get long term brandability and, you lose nothing as your banners still fly along with the themes too
Just a thought, if you had an 'archive' of the themes of sorts, you potentially get more clients skinning GFY to because of the long term branding effects, not just the short term returns on their initial investment
Regards,
Lee