Per the rapid healing feat:
You eliminate an additional stun and lethal hit when you recover (2 stuns per minute, 2 lethal hits per hour) and you get a +2 bonus on all Constitution checks to avoid dying and recover from damage.
Using the hit point system, I'm converting as follows, let me know if I'm off track on this or if you have a better way.
Reduce your subdual damage by an additional +2 for each minute of rest.
Reduce your HP damage by an additional +2 per hour of rest.