I'm a little bit over B too and for halloween I managed to hide them pretty well with a A-cup sport bra with band 2 inch smaller, bandage bound pretty tight, a "slimming tube" wear higher than usual(reduced the definition of the boobs), and a thight tank top. Then wearing a bit larger tops they should not pop that much.
Maybe not the best solution, but the only one I found as mine are still hard as rock they won't slip or squease easily.