Focus-free assist

[thinus]

but macro for each spell of each character... thats not gonna work

You could just make a separate assist key. Its a bit more work as you would have to hit the assist key every time you want the group to change targets but you will save on macros.

What key-copying software are you using? I know with AHK you can send a key before the pressed key. Most of the people using AHK has it setup to trigger your assist macro before triggering the key press. Technically it is not a violation of the ToS as you can already do the same thing in game by creating macros for every ability.