Why not start with a respectable open bar in a hotel that's large enough, like the Sheraton. You can create an identity like you are there for a company or organization party, such as International Assocation of Pipe and Rod Fitters or Cat Rescue (Pussy) LOL. All someone would do is print some cheap identifying badge that you could put any name on. People would mingle on there own. If you want music, change the venue to Waltz where it would be cheaper, darker, more of a club and discreet, but still close to the Sheraton. Then any girls or guys could previously arrange rooms for themselves.