The only reason to install the Comptip on an old mast is for racing. In that case, I recommend buying a used mast with the Comptip installed. Don't "bobbitize" an old mast if you don't have to.
Hobie's free Comptip kit program expired a couple of years ago. I would be surprised if you will be able to get a free Comptip from the factory. A dealer may have a Comptip or two laying around.
My '98 Hobie catalog shows the Comptip as part #20611100, $556. Bet you can find a used mast for that.