If you use attack move with a group of units, and that group has AA trucks, scouts or fabbers, they'll rush in ahead the rest of the group and die to ground units because they have no ground weapons so they don't stop to shoot like the rest of the units do, making controlling armies with these units mixed in frustrating as hell Could you give them an invisible weapon that does no damage and has no effect with a range slightly higher than what a Bolo's range is, so attack move makes them stay in the back line instead of suicide rush with the infernos? It would take very little time and would help gameplay massively
What if there are no other units in your group then he would stand still forever to for example kill a wall.
That's more of an issue of walls being considered targets by units in the first place (I'd treat them like wreckage, where units don't shoot them but you can mouse over it and tell them to) but either way if the unit's just on it's own and you don't want it to get stuck on walls targetting it, then don't attack move your aa squad and they'll act just like they do currently (driving blindly into harm's way to ram the enemy tank battalion to death -_-)
I don't think using an invisible weapon is a way that an implementation by Uber should use, but problem is real and needs a solution, albeit one that is a little cleaner.
This isn't a problem so much as a desire for a more complex behavior than the available tools can give you. Formation movement should theoretically enable this, with the heavy units in front and the support in back, but formations have generally not worked well in RTS games that aren't squad-based. Alternately you might try having the support units 'assist' the heavy units, and then give orders to only the assault units, but you'd need more filtering options when selecting and ordering units.
I generally use move to instead of attack to or attack this commands and the formations that result work well for me. flamers in front, AA in back.