Not an answer to your bore sight question, but I did buy one of those Midway scope mount Level-Level-Level (I think it's a Caldwell...which is just a sub-company of Midway) scope mount tools. They are simply 2 bubble levels mounted in a magnetic piece that allows one to be attached to the firearm and the other to the scope.
They make quick work of mounting the scope with level crosshairs. No guessing.
Now, as for bore sighting with a T\C, or any gun that i can look through the bore, I simply pick a spot at about 100 yards while looking through the center of the bore, then I adjust the crosshairs to be on that same spot. This has always got me on paper at 100 yards, and then it's just a matter of half a dozen shots or so to get it to bullseye.
Dave