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.
"The Constitution is not an instrument for the government
to restrain the people, it is an instrument for the people to restrain the
government lest it come to dominate our lives and interests." Patrick Henry