Sanded the backs of these chrome bumpers and experimented with 2 types of aluminum paint. The left is flat (more gray and still has tape on the edges) and the right is more metallic. Not perfect but they are just the backs so won’t show much and are way better than they were.
This is what I have done... if you have a few threads above and not sheared off flat.
Get a pair of long nose vice grips and grip on pretty hard, not crazy hard.
Heat the vice grip up above the snapped off bolt, but not on the center cap itself.
The heat will transfer into the broken bolt... some spray could help as well, but work it back and forth slowly... will pop out eventually.
Cut off wheel... takes a while and makes a mess, but there was no saving these unfortunately.
New England center caps take a beating and for whatever reason, the fronts tend to survive better that the rears.
The fronts I can't do much with except throw them away when they are cracked/broken, but a little birdie told me something about the rears and I will attempt to make something.