I fragged my bubble into three - it was taking 1/3 space of my 35 gal tank (sorry, the frags were already spoken for). The trick is trying to cut along "seam lines" and not try to rip the bubble anywhere. I artificially introduced seam lines with zip ties for about a month or two before I actually cut to give the bubble time to "adjust."
When I cut, the difficult part was cutting the rock with a diamond saw dremel (no access to a band saw) -- you can't really do much of a curving cut as you'd like - especially since they don't make large enough diameter blades for it. [NOTE: safety mask/goggles is a must since the dremel spins the slush back at you].
Within the month after the cut (i returned the bubbles back to the original tank for consistency of water quality etc), each one was healthy and had increased in size. Once I passed the two frags off to friends, I'm hearing from them that they have nearly doubled in size.
So, yes, it is possible to frag bubbles - just be smart about it.