That model boot had a 4mm and 6mm insert that replaces the flat one that is currently on the boot. The oversized 4mm and 6mm replacement inserts had deep countersunk holes so that the screws are safely below the surface. You then use the jointer to cut whatever cant angle you need into the sole, and counter the top of the lug to bring the sole back to DIN standards.
The rub on this great idea is that at this time you would be hard pressed to find a shop that has any of these inserts left. I do not think that Tecnica has any of these left in their inventory.
There are a few shops that would be able to use a 3mm lift plate with a cantology shim. You would have to have a plate that does not interfere with the existing screws, as well as an angel looking over your shoulder when you go to cut the upper ledge of the boot sole lugs. There would be a risk of that happening if you went thicker than a 1.5 degree shim.
So for the OP to get a 2.5 degree cant into that model boot, you would have to have a set of the 6mm shims and a boot guy with bigly jointer/router skills...