Of course, I think it's fun to ask GT members for ideas on how to achieve our naughty hopes/fantasies.
Your description of the friendship is very well laid out.
I hate to rain on your parade – or perhaps you'd like that 😊 -- but I see any "pee-on-me attempt" as quite likely to call your sexuality into question, and at worst, permanently damage/end the friendship.
Perhaps you could go on Grindr or other app and search for a bisexual guy with your roomie's general "look," who would accommodate you.
Weigh your decisions carefully, and good luck!
Your advice and knowledge is spot on. Don't cause permanent damage because of a fantasy.