I explored this idea with Craig at Hill Archery a couple of years ago. He was against the idea as he felt that it weakened the riser and left the bow vulnerable to breakage from sideways shock, like if you bumped it into a tree or something. His recommendation was what No-sage said... just slip a thin leather rest into the wrap on the off side and shoot it off of your hand. Takes a lighter spine, but works very well. I actually build about a third of my bows with no shelf at all so that they can be shot off the hand from either side.
Here's a pic of what I'm talking about:
The leather "rest" doesn't need to be as deep as a shelf. All it is is a reference for arrow placement, and the leather piece also provides a swelling that provides muscle memory for your hand placement.