BTW, if you are worried about splitting him apart in back, you might be trying to get too much in there. Or, it could just be that balloons were hard to work with.
Remember, I only used 1 cotton ball. You could probably find room for more, but remember you aren't trying to give him Bane traps, you just want to fill that gap between the suit and the cowl.
Break the cotton ball up into bits and push them into place with a q-tip... hope you have one of those...