Is the reason why it's rare to see tied and gagged whores fucked on film that it could look like rape, and therefore break some stupid laws? Don't think I've ever seen a really really good scene like this (russian crappycam footage doesn't count).
Tie her up, gag her so she can't say no, and fuck her silly. If whore safety is the problem, just do what I do in similar situations at home, give her a bead or scarf or something to hold on to, and letting go of it counts as the safeword. (although that would make it even funnier to see the whore all wideeyed if you continue after that :P)