It is possible that the process could be scripted.

Work flow:-

For each polygon in the model.
Does polygon intersect the ground? If so move lower verts to y = zero.
Is polygon below the ground? If so assign to a discard group/material.
Perform some Poser Python sleight of hand to effectively delete the unwanted portion.

The Scissors script will do it. I guess with some manipulation that could be adapted to batch process.