Just find a relative attractive girl and have her sit there and then have the men jack off to her. Otherwise you are going to have a very tough time selling the scenario of the guy jacking off with just you.
Bait and switch won't work here either.
I did this when auditioning some guys for scenes, purpose was to test their nerves.
It made me smile as she sat there and they would just stare at her and then unload on the coffee table.
