The trouble with epoxy is that it is likly to be stronger than the resin it is holding together, plus the nature of resin usually mean its binds very tightly with the epoxy.
Breaking that bond counts out most of the normal methods I'd use, as Chrome said, these would almost certainly cause damage to the resin. I can only find methods of removing the glue using acetone, which will also melt the model, so its a no go. Very hot water may help to loosen the resin, but it is likly just to either do nothing or worse deform the shape of the resin. Splitting the pieces by force will probably crack the resin around the glue joint, but not the epoxy joint itself.
So not very helpful at all really, but would be interested to see if anybody else has any other ideas.