What I do for stag is to get it as thin as possible by grinding off as much as I am comfortable with on the side that fits next to the tang. At first it may look a little too thin but you will surprised at the outcome.
I clamp or super glue one scale to the tang then drill through the tang then through the scale. I then turn it over, leaving the "freshly drilled" scale attached. Attach or clamp the other scale and then drill through the first scale, tang then the new scale. The reason for leaving the first scale on is that if you don't, your holes may not line up from one side to the other. For irregularly shaped scales like stag, I will place a rag underneath the handle. This will sorta comform to the shape of the piece and you can drill a pseudo straight hole. Be careful when the bit breaks through and make sure it doesn't grab the rag. Things can get pretty excitin'! By the way, a drill press or at least a drill stand is a must for doing this.
After drilling the holes,if super glue was used, it give the stag a good rap on the workbench and they come off. Clean up the tang and scales then pin or bolt and epoxy. I use acetone for clean up.
