Ive seen it done before, with variable success rates. Id suggest a band saw or a tile saw. Most of the time those corals have lobes that pinch together somewhat- those small gaps are where you want to try and separate it. Ive heard some suggest that you should take a razor blade and cut the tissue clean over the spot that you intend to saw apart to reduce the trauma to the actual tissue from a spinning blade... and if I were trying to frag the piece, I would probably do that too.
If you decide to try it, post pics and updates, would you please? Its just not one of the more commonly done corals.