I'd personally go with an oracle. You can get the healing spells by default but you can really tailor your spell choices to be whatever you want to be. Depending on your mystery and spell choices you could be a front line fighter, a blaster, a controller, a buffer. Really whatever you want. I'd talk with the guy playing the wizard and see what role he is planning on filling and then you can build to compliment.
Druid can also be a good choice. Again they are a flexible class with the added benefit of being able to change your spells every day.
Ehh, to do your job as an out of combat healer probably, you'd need to pick
2nd: Lesser Restoration
3rd: Remove Blindness/Deafness, Remove Curse, Remove Disease
5th: Break Enchantment
That's more spells known that I'd personally feel comfortable spending on healing. If you want to do the off-healer thing, do druid or cleric. That way you can prepare them after you find out you need them instead of having to lug them around all the time when you don't.