I have that. I'm using a rogue as primary since thats my main. the rogue doesnt need to go behind or anything. I just want 1 which is the rogues primary spam to press the 1 and then have my shadow priest assist and do a cast sequence macro. It's basically just to speed up some dailies. Assist works if I do alt - backspace in the main window but not when its attached to the FTL DPS 1 key. The macro also seems to work by itself just not all 3 together.

Its the following 3 commands attached to dps 1:
FTL Assist me -> Target: Current Window / Keymap -> General and FTL Assist Me
1 -> Target: Melee characters -> Key Combination: 1
My named macro -> Target: Casters