Easy enough, hell I can give you letters if you want
You and your quick hacks
I actualy have a second heightmap used for the plates themselves, this is what gets added to the base heightmap to create the mountains and basic landmass shapes. A 'hot spot' is a point where the surface plate is weak or thin (relatively anyway) so I can calculate accurate hotspots by picking the lowest points on the plate height map. Why fake it
The only thing you'd need to do is make sure it looks good in the game. For example if you found a hot spot in the ocean you'd wouldn't want to create a land tile without making its eight neighbors into coasts and making sure all of the neighbors of those new coasts were either land or ocean, but never deep ocean.
To keep things simple, I could check for that when generating the map and make sure all 'hot spots' were not in deep ocean tiles. Hell, we could even get a new feature or improvement sort of like the existing 'smoke' except white, and place it on any peaks or hills that were also hot spots so you could identify dormant volcanos. That way you could actually do some damage with them when they blew
Edit: Should we continue this in the RiFE forum?