pretty much what Ualaa said.

I would drive with the SHaman indeed, and just have a specific key to tap (press rapidly) to move the mage a bit and therefore break follow.
Typically I use my formation key to break follow.

fights will look something like this:
- find suitable target (mage is following shaman)
- get within 30-40yards of target (mage following shaman)
- tap your formation key (mage moves 1yard left/right/back/whatever, shaman keeps running to mob)
- attack mob with both toons. (shaman melee, mage ranged)
- Once the mob is dead, tap your follow key and repeat.