Here's an idea: A can-buy-only-once type of item for Ts, costs 1 credit, that fools traitor testers. The catch is, if you are stuck in it too long say 10 seconds? 6 seconds?], it starts beeping like crazy, revealing you're a T, requiring luck [not being locked in it, or stuck otherwise using it too long] and strategy to use correctly.
One problem though, I'd guess, is being able to make it work with T testers, since I'd guess they aren't all programmed the same.... damn, sounded like a great idea though.