I cannot actually see a problem with #2, it would be my preferred solution. When I go to trade shows / conferences it is to talk to brains, not bodies, the sex of the brain is immaterial to me.
To me, making sure the bodies are 50% equal in gender means nothing if 80% of the female bodies are only there to make up a body quota but have no interest / knowledge of what is going on.
Maybe change it slightly so that the rules state anyone at the booth must be a full-time employee or a contract employee with X months at the company.
Could you go into a bit more detail about your reasoning for #2 not being suitable?
[EDIT] Messed up my percentages
My proposal is purely to get rid of the "Pretty face, no knowledge, hired solely for the event" style of "booth-babe".
Of course companies could hire people for the require X months but I am hoping the monetary aspects of that would discourage them.
Also, enforcing the proposal would be tricky I think.
Here are our options:
1. Require a strict dress code for booth babes as to not offend anyone with scantily clad women. Result: we can't tell booth babes from technical females.
2. Require everyone working at the conference to be an active and knowledgable employee of the company which has purchase the booth space. Result: number of females on the show floor drops precipitously.
3. Require a 1:1 ratio of males to females. Result: booths are understaffed or companies don't even bother showing up.
4. Wait until ratio of males to females in the given industry is 1:1. Result: conferences cancelled.
If I was a female, and I'm not, I would be insulted that other females were trying to stop me from getting a job. I know a lot of girls who work as "booth babes" and they are busting their asses just as much as any of us are. It's not easy traveling around and standing all day long in uncomfortable shoes for pay that is slightly better than peanuts.