MAPP is a fuel meant to be used with oxygen in a torch. I doubt if it would work with a carb set up for propane, as the vapor pressures and oxygen requirements (hence air requirements) will differ. You'd still be limited by the amount of air the engine could suck in.
IMHO, I think nitrous has a different affect, being an oxygen source rather than a fuel. It provides more 'oxygen' to the mix in the cylinder, allowing you to burn more fuel per stroke.
Why not just cut down the transom on your dink and put a row of 3 or 4 of those propane fired babies across the stern? Run them all off a 20# grill bottle.