I'm planning to buy my submissive girlfriend some nipple clamps, and I want her to wear them under her clothes. The problem is she wears a 40 GGG so she HAS to wear a bra. Are there any good clamps that I can get her that she can wear under a bra discreetly? These are not discipline clamps, they are for reminding her of her role. I will be getting another set for discipline. Also, how long can these kinds of clamps be worn safely?