Clamp the sidestand to the frame so that when folded up its parallel to the frame and doesn't catch anything. Lower the stand and pack the foot with a scrap of timber until the bike is at a reasonable angle and measure how much you need to lengthen the leg. What I've done on both my B33 and B40 is to cut the leg part way along, thread both ends internally to fit a threaded bar of around 5/16" diameter, make sure the foot is at the correct angle, then weld the joint to make it completely solid. Once the weld has been ground to the correct profile and painted, you'd never know anything has been done.