Hi,
that's very tricky to do actually, and it ipens a can of worm when you try for several reasons.
I would first look on the asset store for assets doing this. If you find one that is doing what you want, let me know and I'll look into this and see if it can be controlled with PlayMaker with few actions.
typically your problem is the fall off system so that when you dig, it's not just the face undert the ray you move but an area using a fall off curve or math to create a hole shape that is suitable for your needs.
Bye,
Jean