Okay, if it were me and I was the only guy who went to any old party, I'd probably be fine, but being a guy invited to a
female-dedicated event would totally ruin it for me, no matter how good a relationship I had with the women involved. It's more about the dysphoria than anything else, and I totally get that.
You're in a tight spot though. For me I would either say no, or come out and say something along the lines of 'If you still want me to come as a close friend then I'd be happy to, but please don't expect me to present or act as female, and don't bug me when I choose to opt out of the spa-treatments.'
If you can't do either of those things though, take some 'extra-manly' things with you (fishing, sport, or motorcycle magazines, toy car construction set, etc) to recharge the man-battery at the end of the day, and help you feel better after all of the lace and fruity cocktails.
An awesome coping mechanism that helps me deal with dysphoria in a similar way to this is having something small and 'manly' (toy car, marble, multi-tool) in my pocket, as a sort of talisman that I can fiddle with when feeling uncomfortable or depressed. Really takes the edge off.