Creating a pocket in the heel for a bump is really hard to do unless you have the right tools or the material on the inside of the heel has enough thickness to make a pocket. If not the latter (first skates I dd this on were pro spec apx2's that had very thin inner heel material), the heel is a very reinforced, circular area and it takes a lot of pressure to make it move. Typical punches don't work because they actually push the outer area of the punch inwards in the heel whilst you get a little bit of movement in the middle of the punch ergo no result. You need a punch that is shaped liked the heel for the punch to work or you can do this: I made a frame that clamped and locked the boot into the middle of it and attached another frame that sat outside the quarter panel where I wanted the punch to occur. Then I used a c clamp to pull the heel area at that spot out with heat added. You need a lot of pressure to get the heel to move so you have to be careful here with the heat and pressure or else you can distort the shape of the heel. This worked ok but it is a slow process. I now have access to a 3D printer and I print up a punch according to the boot size, heel shape and position of the punch. Good luck with the tissue process but I wouldn't be holding my breath, heat and pressure will most likely give you the best result.