A second slug on the halyard would be OK if you leave the beach with the sail already reefed. But trying to reef once you are on the water on a pitching deck with big wind AND having to put the slug into the fork slot is a little too much to ask, I think--this was the complaint of the original poster...to reduce sail in a dangerous situation, one has to perform a dangerous act because of the fork. For the few times that reefing may be needed, it will be "OK" to have the 2:1 on the halyard since with the sail lower, the compressive forces from the halyard and mainsheet/downhaul will be acting further down on the mast and will be less likely to put the mast at risk. Someone mentioned that part of the reason you want this fork is to keep the mainsail in the groove at the top...a simple slug sewn into the headboard of the mainsail will do this just as well.
A halyard with a second stopper would be too long. NA Hobies try to insulate the masthead with the comptip. A halyard long enough to cleat at a reef point could conduct electricity to the metal mast and to a person stepping it and defeat the safety purpose of the comptip.
A headboard slug will not work on a Hobie Comptip mast. The sail track in the comptip is too soft to take the leech loads. The headboard slug would pull out of the comptip and probably jam at the end of the comptip if you tried to lower the sail. The standard halyard lock system keeps the head of the sail high enough and close enough so the leech loads are taken by the halyard not the track.
In areas of the world that still allow an all aluminum mast reefing is possible and a dual stopper halyard is used. Look at old Hobie pictures to see reefed H16's and note that the new sails used in European championships have reef points.