I also thought of that - though I was on the "maybe an easy way to have softer shadows" trip

For now I've got another issue to solve with this one but, at the moment, I don't have a clue on how to do it.
I'd like to as well implement a section in the function that takes care of wide vertical gaps between the vertices. That is, if you place a grass model on a high cliff or sth. similar, but the model does not exactly fit the cliff's shape but is hanging over, the grass on the floor will be connected with the grass on the cliff via strangely stretched polygons, as the model can not be sliced in half. I thought that maybe you could measure the z-distances between the -already adapted- vertices to find such cases and then... well, I have to waste another thought on how to make the appropriate vertices somewhat invisible. If anyone has got a clue on how to do this, any hint is welcome!