I always drill trough the bottom layer. When drill went broken, I could see it in the hole, but these was no any change to pull it out. First solution was use blade mounting screw to push the drill bit deeper. I was already celebrating when screw went without any problems and blade mounting was secured. When blade mounting was finished and I did remove skate from blade mounting stand, I realized that heel is not solid. Drill bit was in the cavity and was keeping rattling noise.
It was clear that I cannot leave boots like that. First I though, should I inject some glue into the heel so that it would hold drill bit so that its not rattling. After thinking some while, I concluded that I cannot fill the whole cavity space with glue and if I do not fill it, these is risk that my gluing trick wont last long. I decided to take another risk and I drilled about 8mm hole in the middle of the heel so that blade heel plate covers this hole. I was able to pull that drill bit out trough that hole. Boots worked fine until they were scrapped from another reasons.