I haven't needed to do this, but here's what I would do if I had to:
1. Purchase a used sidestand. (I'd rather have a good one on had in case I screw up the modification, or if I want to put everything back to stock.)
2. Place plywood shims of equal thickness under the front and rear tires until I get the lean angle that I want.
3. With the bike still on the sidestand, mark two points on the shaft of the sidestand, the VERTICAL distance between the points being the same as the thickness of the shims. The actual distance along the shaft between the points will be greater than the vertical distance, of course.
4. Remove the marked sidestand and chop it, removing the material between the marked points.
5. Have a welder weld it back together.
6. Get it finished however I like and re-install.
Exactly....

Key point is getting a good one as a back up I think.