Question says all. The prob is that the sim you're visiting with is gonna be a playable, too, so I wouldn't want that one zapped off...

Sure, just ban them by name. So sim you want banned walks onto the lot, add them to the list and delete them with the hand tool. I can't remember if that's on the visitor controller or on the business selector from MATTY, but at least one or possibly both those mods can do it. I did that at my tavern, banning noble ladies one by one as they showed up. I had the queen get drunk and try to propose marriage to a townie so I started the banning after that lol.

Visitor Controller from Simbology can do this and more. http://www.simbology.com/smf/index.php?topic=17.0

The simbology one is very useful. You can ban NPCs, townies, downtownies, non-locals, pets, and others. Banning playables will stop them all, except whoever you are controlling at the time, along with any sims you take along, including groups or a date. You can even ban a lot from everyone and use it as a private group or date place.

OK I dunno why I didn't come up with just banning the playables one by one.