I was doing that with my pally team, using a high level to run them through instances and I found they really nerfed the rewards and I was only use a 70 warlock.
Once I found out my pallys were pretty awsome and could do most of the instances themselves and quit doing the boosting runs.

but if you must run him though instances get him to level 20 and switch to SM, the higher level instance should give better rewards.