I don't understand why you think there is some sweet spot for a professional event where a sexist joke can be appropriate.
Problems with your rewrite: Women: Yes, we aim to make a welcoming atmosphere for women who want to participate in our hackathon. (And for those men still afraid of getting out-programmed by a girl, we've hired an all-female event staff to serve you cold beer.)
1. Boys and Girls are children. Men and Women are adults. The target audience for professional events are people.
2. You imply that being out-programmed by a woman will hurt a man's ego. This is outright sexist and perpetuates the idea that men should be better than women. It both degrades women and shames men.
3. It creates a hostile environment for a woman who programs well. By outing herself as capable she will create social strife with her male peers. There is a reason women do worse on math exams in the presence of men. Social pressures is a real thing that you, as a presumably straight white male, get to ignore.
4. Pointing out you hired an all female staff makes explicit you cater to straight men.
5. By prefacing it with "Women:" you are still listing the female servants as a perk. "Great Food" Is a perk. "Handed to by a woman" is not.
The entire concept literally uses breasts and vaginas as a lure for men. You keep trying to force the idea but it won't ever work in an inclusive way.