Ok, so if anyone's interested, I discovered/created a VERY consistent way to do this without creating any fancy button shortcuts. Message me if you're having trouble with iagA and I'll explain it to you. It should be noted that I play on a stick, not a controller.
For pad players, at least for me, I map out a shoulder button to a bind like A+B to R1/RB or R2/RT. Then quickly slide my thumb from A to G and hit the shoulder button accordingly. It should register as agA/iagA if fast enough.
For stick players, I assume just having 3 buttons in a row with A G and another A input and gliding across fast enough to register an agA/iagA.