I had her purchase a chastity belt a while ago...with the stipulation that I would buy a stronger lock than it came with. It was one of those cheesy little locks that came with the device from a sex shop. We haven't gotten around to using it yet but I'm anxious to see her wear it during a full shift (she's a bartender).
They also make some very nice nipple clamps with dangling vibrators that would work nicely under a loose fitting top.
Seems to me I've seen a thread along these lines before