Shaving the actuator should work regardless of the stick type... I have some supers to try it with, so I'll start there.
I did something very similar to this on my first attempt.
I took a Happ Ultimate, which is supposed to have a square actuator on it, and built a round actuator of the same diameter.
That kept it from hitting the diagonals unless you were dead on one.
The problem with using an 8-way stick as your starting point is that it won't guide you to the true directions.
You still get the 8-way feel to the stick.
It does make Tron playable however.
The main problem I see with shaving the actuator on a Super would be that you would be increasing the amount of dead space in the stick, making you have to move the stick farther to hit the true directions for every bit you shaved off.
Using a diamond-restricted 4-way as the starting point, and enlarging the actuator would actually tighten the stick up, and would be the preferable route to me.
For those who already have DOT/Xeno sticks, and have minimal woodworking skills, the method I described above works great.
You don't even have to be ultra-precise about it because the large diameter of the stick will smooth out small imperfections.
You just need to make sure that you get the center hole close to center on the piece.