From the most I've read here, most groups are made of 1 melee and then x number of casters/healer. If you are Duo'ing a Warrior and Shammy, I suggest your shammy goes caster/healer and justs keeps away from the warrior as much as possible tbh. What I think you are trying to do is have your shammy melee the target too which is ok if thats what you want, however you are going to run into a load of problems with things.

You can't get any closer on the follow command than default. You would have to assign a key to nudge you forward into melee range after the warrior charge, you could combine a warrior skill that you use after charging to your shamans forward key (or alternate forward key) so that your skill sequence would be,

Warrior: Select Target, get to distance, CHARGE!
Shammy: Trondle up behind.
Warrior: Sunder Armor (Shaman) Forward
Shammy + Warrior: PWNAGE!

If that made sense to you, cool, if not, great because my work mates are like wtf too.

I highly suggest ot make things easier for yourself, to put your shaman as caster/healer buddy and duo it that way, would make things a load easier for you. If you did that, your sequence would be much simpler:

Warrior: Charge etc etc as before.
Shaman: As before.
Warrior: Sunder Sunder, same key for shaman - cast sequence of Shock and Bolts.
Shammy + Warrior: Same as above but much easier.

Hope that helps.