The isolators are two peices of metal with rubber vulcanized inbetween them. You can't make them shorter. However, if you were to burn out the rubber, weld the two pieces of metal together, then figure out a way to mount a monoball in there, you might be able to lower your ride height by at least 1/2" or so. Not much.
EDIT: If you were to mount the monoball on top of the isolator, that would drop it even more.