Sorry. When you said aim I only assumed you meant the direction, not using tilt aswell to be able to determine height.
Basically, it works just like FIFA10 (you can still use the manual or semi aiming schemes), only instead of pushing the stick all the way in a direction to aim in that direction, you would only tilt it a certain degree.
There would need to be a deadzone in the middle due to the small movements involved would make aiming very inacccurate with tilts less than 30 or so percent.
The more you tilt the stick, the higher the intended shot.
Tilting 30% or less means you basically want to achieve a grounded shot or long pass. Pushing the stick 100% should give a sufficiently high shot or longpass to be able to replicate the highest variants of either type.
To be more effective and usable, the intended shot height would be restricted to a more conservative angle (to avoid having stick tilts between 30-50% being from ground to bar, and everything over 50% being hitting various constructs at the top of the arena.
Long passes using the Long pass button would have a higher maximum angle, to make sure you could do the sort of semi-chipped longpasses you can do in real life.
To be able to execute very high, or almost lifted lobs and such, you could use LB+Y lofted through balls as the highest trajectory of the 3 types: Shots, long passes, lofted passes.
So it could look something like this:
Shot button: intended angles possible - 0 to 30 degrees.
Long pass button: 0 to 45 degrees.
Lofted through balls: 0 to 55 degrees
For any situation you could use either of the three shot types to determine the basic type of angle you want, and then freely modify it with the tilt before the strike.
You could also use the long pass button as a shot button, because a low stick tilt angle and a hard power will basically yield a laces shot. Increasing the tilt of the stick will make the player use his foot more as a wedge to achieve a higher trajectory.
This system could also be used for long passes of any kind, so that you can freely vary between lofted and driven variants.
Essentially the idea is to not use contextual ball strike types, but allow the player to freely intend to get any ball strike type in any situation, for any purpose.