Personally using the face buttons then inputting something on the controller isn't something difficult in the slightest. I'd suggest giving it a try in the nets just to see how it feels (even though it does nothing right now, unless you hit 'A' or 'X' depending on console), it is remarkably simple to do, doesn't take very long, just that split second extra premeditation (which you need for unorthodox shots anyhow). Just to clarify, it would operate like sticky keys, you press it some time in the run up, and the modifier is on for the duration of that ball.
The difference for leaving though is it needs to be an instant reaction. You need to be able to be able to just do it reflexively, and I don't find any of the options particularly good for that at the moment.