You could just wear a wrist brace from the local drug store to make it clear that hand isn't used for hand shakes. I wear one 24/7 anyway to avoid tightness in my wrists from too much coding.
Yes, that works well with short sleeve shirts, I have a BOA brace that I use for watersports. You'd be surprised how many folks will give a hearty handshake to someone wearing a cast, though. http://goo.gl/zeT40x