Heat is certainly an option, to be used with caution (for obvious reasons).. Another would be to load up the puller again, and give it a good hard smack on the puller screw head... the shock might break the prop free of the taper. Soak it overnight with penetrating oil too.
If you do try the hard tapping method, do not stand directly in line with the shaft/prop when you do. Even better, leave the nut halfway on - the space between the nut partially threaded on and the prop will be plenty break free on the taper.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)