This whole problem seems odd to me. In the groups I play with, we try to avoid "whack-a-mole" and start healing people when they hit half hit points (the point at which they are taking visible damage according to the rules).
If you think there are no consequences to "whack-a-mole" healing then you are being to lenient as a DM. Start taking attacks on downed PC's to inflict auto-fails on death saves and they'll see it as something to avoid at all costs.
If you think there are no consequences to "whack-a-mole" healing then you are being to lenient as a DM. Start taking attacks on downed PC's to inflict auto-fails on death saves and they'll see it as something to avoid at all costs.