I think Ison have a guide and drill bit as a workshop tool to sort the job oot! I used to have one when I worked in the shop
Dam should had one for me self :!:
what you could do is saw a slot across the top of the bolt so it looks like a flat head screw ( only go down about 2 mm) then using a flat blade screw driver try to remove the remains of the bolt and then file the brake boss end so no sharp edges are left