I don't think that there is much you can do except not to honk on the sticks so quickly.. When a wing exceeds the critical angle of attack, it will stall.. If you are moving fast enough in the horizontal direction and have a small yaw moment at the time of the stall, you get a snap roll. You could try less deflection of your elevator, slower thumbs, or maybe moving your CG back a little bit.. If you have a forward cg, your aircraft will trim out in level flight with a higher angle of attack. When you are level at a higher AOA, you are closer to that critical angle of attack where the stall will occur.. With an aft loaded aircraft you will need a little nose down AOA to maintain level flight, keeping you further from your Critical angle. Of course moving your cg back too far will cause you more problems than you may be in the market for...

If your airplane has a split elevator are you 100 percent certain that they are moving in harmony with each other? If there is a difference in travel, this will give you enough of a roll/yaw at the stall to send you into the "snap"...