One simple solution would be to change the target line from one creature to one ally. Thus the cleric could not use this on himself; and only in limited situations (coincidences of chance, or more likely munchkin players who would find a way to exploit the rules anyhow) would it not cost the cleric in healing surges.
Even with a means to gain regeneration each 'encounter' (as the short rests become), I think most encounter regeneration powers such as longtooth shifting only work up to bloodied value, thus it does not remove all resource cost from the healing.
At least since it doesn't use a healing surge, it can't be further enhanced by pacifist healing; though there are ways to enhance it...
Student of Artifice + Potent Restorables (2 feat cost) adds +2 up to +7 (level dependent) to all healing powers.
Healer's Implement (1 feat cost) adds the enhancement bonus of your implement (+1 to +6) to cleric healing powers.
Healer's Brooch (neck slot) adds its enhancement bonus (+1 to +6) to your healing powers.
Compassionate Healer's (paragon path) 11th level feature 'Compassionate Blessing' allows you to suffer an extra 5 points of damage to restore 2d6 extra hit points (and is worded so that it could still be self applied, if Life Transference can be self applied - risking 5 to gain an average of 7 not a bad risk)
So, depending on how you consider the implement/brooch stacking (some argue since you are using the enhancement bonus of the item, the bonus IS an enhancement bonus and they can't stack; others argue if that were true, similar wording on dozens of weapons that allow you to add the enhancement bonus to attack or damage rolls would be pointless, thus they are untyped bonuses simply based on the enhancement bonus of the item (such as how other bonuses are based off of an ability score but do not become 'Charisma bonus' or 'Wisdom bonus'), and do stack); you are looking at healing up to twice your surge value, plus your wisdom modifier (Healer's Lore), plus 2d6 + (13 or 19), all for suffering your surge value plus 5.
Given the 26th level minimum for that (Potent Restorables / +6 items), you're looking at a surge value of (assuming CON 10 to start) 37, a wisdom (assuming 18 to start and all level bumps in wisdom) of 25 (+7).
So you suffer 42, heal an ally for 96 to 106 (or if you're stacking the two items, 108 to 118). Assuming you weren't bloodied to begin with, you do this a second time for another ally 5 minutes later. Then you're definitely bloodied (down at least 84 out of 149), and so you repeat this for yourself on the third 5 minute interval... of course you ultimately only gain from 54 to 76 (depending on the dice and stacking), since you hurt yourself again first... you're definitely not fully healed here. But you can now do it at least twice more before hitting unconscious; so one more ally then yourself again. You've now passed 25 minutes, and you are only down somewhere between 16 - 60 hit points (again, depending on the dice and stacking). You've also healed 3 allies for 96 to 118 HP each. An extra 5 minutes sees you nearly (or more than) fully healed as you repeat this on yourself one last time. So ultimately, 10 minutes per ally to heal them 107 (average) hit points with seemingly no resource cost!
Except time IS a resource too! What if you have to save the princess in only 2 hours? What if there are some goons chasing the party, and if you stop for more than 5 minutes, they catch you and combat starts? What if you're in a hostile environment that saps your power (hit point damage, lost healing surges, cumulative other debilitating effects) the longer you remain there? What if the artifact you are hunting will be gone in 20 minutes, as the dragon decides that you are too powerful to face and flees with her precious?
Yes this can be very powerful, especially if a player builds the character to focus on healing. But is it at all game breaking? I don't think so! Just as certain attack powers (when similarly focused on) can seemingly alter the face of some (or most) combats; a nova ending said encounter in one or two rounds versus 6 or 7... thus negating a similar (or greater) amount of damage the party migt have suffered . . . with seemingly no resource cost!
It might force the DM to become more creative, to take into consideration his player's powers when designing adventures for them... BUT ISN'T HE SUPPOSED TO BE DOING THAT FROM THE VERY START?