If you don't want to put an extra slug on the halyard, make up a strop of vectran, dyneema or wire to go between the head of the sail and the shackle point of the halyard. so that you still use the same slug but the sail is not hoisted so far.

Best not to just tie the halyard off on the cleat, you still need plenty of downhaul to keep the boat well under control when reefed.