I believe George Willer had made a tapered reamer for that, but all of that requires a pretty good machine shop both to make the reamer with the original taper, and then making the hole at the correct angle. Unless ou intend to do it on a regular basis it is cheaper to buy another spindle. Many of the people on the site will have them. If the bolt is broken off in yours, just insert a punch in the hole on the back side and tap it out.
If you are not part of the solution,
you are part of the problem!!!