I often Dual-Box my mage and my hunter, with my mage as lead. My hunter has skinning and mining as professions, and after pondering over how to do it for a while, I came up with this macro for making my slave skin the mob I just killed.

/target Leadcharactername
/cast [target=targettarget, exists] Skinning

It works like this:

1. Kill the mob, 2. Loot the mob with lead, 3. Target the dead and looted mob, 4. Hit the macro button. Your slave now skins the targeted mob.

If you kill more than 1 mob in one go, then you just loot them all, and then go over them targetting the dead mob and skinning, or just loot, target skin one and one.