I don't know why I'm bothering posting this since H&H won't see another update for ages, but it's a decent and simple idea.
You should be able to create boulders (the things you get when digging out a cellar), from landscape rocks, simply for the fact that having useless runestones all over the place when you're building your village is annoying and boulders still offer some worth with being movable sources of stone.