Ability to tell MapMagic not to generate a chunk

Perhaps in a pre generate / prepare callback, ability to return whether or not mapmagic is to continue generating a chunk.
I havn't found any callbacks as yet in MM2, but perhaps a little like this...

enum GenerateOption{
Normal, // carry on as normal.
Skip, // skip generate and leave a big hole where the terrain should be.
Referrence // use the ref terrain passed in the callback method
}

GenerateOption OnPrepareStarted(Terrain terrain){
// User code
// do stuff to see what we want to do
terrain = LoadTerrain();
return GenerateOption.Reference;
}

or

GenerateOption OnPrepareStarted(Terrain terrain){
// User code
// do stuff to see what we want to do
….
// Do nothing
return GenerateOption.Skip;
}

Hope I explained this well enough :)