Jun 20th 2007 4:35PM I only rolled a Hunter recently but I find the following quite usefult for feeding:
/cast Feed Pet
/use 4 16
What this does is similar to what you described. But except for using an exactly specified item it uses a bag slot. I don't guess you will be feeding your pet Cured Ham Steak forever!
The first number is the bag. The backpack is always 0 and the other bags are 1-4 (5?) from RIGHT to LEFT. The second number is the slot, going from the TOP LEFT to the right and then on the second row from left to right also, etc, starting at 1. So in the above sample I would feed my pet whatever is in the last bag slot of my last bag.
You can always make sure that in this slot is the food you want to give to your pet, whatever the food may be, and you won't ever have to change your macro! (Except for when you change/upgrade bags, which probably happens less often).