Some progress that I will share here:

The obvious answer to how to create a v-bit was to give a bottom diameter and radius of 0. I still don't understand how to limit the depth of the cut. It appears that it will cut to the depth of the flute length. For example, if I have a 3/4" 90deg bit I can only engrave circles that are more than 3/8" (the flute length) in diameter. Anything less and the bit will just plunge to create the circle. I suppose I can play with the tool definition to limit the depth of cut.

I'll keep working....