I did, twice, after a lot of begging ( by the other party), and a full explanation that there would be no sex involved. I have been asked a few times by strangers on this site. NEVER AGAIN. Gay or bi guys may not see why-- in fact, I am quite certain they don't, or maybe they don't care, but they are NOT WOMEN. I add the emphasis because gay or bi people seem to see sexuality as fluid, and the barriers to sex or sexual activities with them as merely psychological, but...as a completely hetero guy, that's not the case for me. If a woman I truly cared about asked, for a threesome with another guy, the answer would be the same. If my best male friend asked, I would answer the same.
Women are different. Even if they are hardbodies, they are completely different from men. They may be "missing some equipment," but they definitely have compensatory additions. Wonderful additions. Soft, warm, inviting additions--both fron and back. Sexually, I view males as almost a different species. Great to work with, ride bikes with, etc., but a species with which I do not care to interact sexually. Apologies to any here here who thinks other species are just fine, such as goats.
https://goo.gl/images/DFnP7j ( even the goats don't like it)
(& if you've never seen the Monty Python skit, it's terribly funny)
(Just in case there's a gay or bi guy out there who wants to play, don't ask.
What part of NO! don't you understand? I've been trolled a few times by people here, so...)