Livingston had one on the boom once...I think he used a batten to extend the boom and mount the spot to. If memory serves me, I think the batten broke in a capsize or something and the spot was lost. I would be a little careful with the nuclear gybes but it's probably one of the better places for it.

For the Everglades challenge, we strapped the spot to the boom on the tri just in front of the mainsail strop. It seemed to work just fine from there.