If the bubbles are completely spherical so that you can't just pop them back out from behind, here's a trick:
Assuming they can be removed and reattached without damaging the costume, remove the bubbles, place them in the freezer for about 30 - 45 minutes (enough to make them nice and cold), then let very very hot water run into a bowl, and dunk the bubbles under, letting the hot running water run over them. The sudden pressure change due to the cold air inside meeting the hot water outside, will cause it to expand and pop the bubble back into it's original spherical shape. I used to repair ping pong balls this way when I accidentally stepped on them.
