The one problem I think you may run into with the variable target system Chazz describes(unless I completely missed it!) is that occasionally your characters are not sync'd up in the group. What I mean by this is, Character 1 is slot 2 for Character 2, and Character 2 is slot 3 for Character 1.

This means that you cannot properly drive with both characters, you pick one, and if you run with the other one your slave follows and assists the wrong person.

With the Chazz system it seems to me the solution would be to define a second toggle key and tie each character to its own ATG. Toggle 1 cycles party 1 through 4 for others in ATG1. Toggle 2 cycles party 1 through 4 for others in ATG2. What this should do is only send the appropriate assist keys to the character ONLY if they are not the focus.

If you haven't run into the issue I am describing Chazz, it seems rare but it does occur where the party re-orders and your characters are not sequential in their positioning.