miami_warrior .... since you're not looking for folding passenger pegs
an effective solution would be to modifythe existing Warrior peg support bracketthat mounts to the frame. With a grinder or Dremel cut-off tool you can remove the welded short U-channel that is a steel fabrication. Grind the exposed surface flat and drill and countersink from the rear of the bracket for a 3/8"-16 flat head socallen screw. Rattle can paint the ground surface and use some blue thd lock on the high strength allen bolt
Modify these brackets: http://flickr.com/photos/[email protected]/sets/72157602601839146/detail/
Another easy solution is picking up 2 or 4-SS or chrome/steel spacers to use as stand-offs to the frame with the stock bolts. A pc of 1/8" steelor 1/4" thk aluminum mat'lshaped as a tear drop drilled to matchthe frame (1 or 2 holes)and an additional hole for the 3/8"peg.
Either of the above will be less involved than cutting a thdIMO.
You can also just open up the M10 x 1.25p frame hole very veryslightly. The tap drill for that size (M10x1.25p)is 8.8mm (0.3465") so there won't be much stock removal and the 3/8"-16 is probably 0.010" undersize. You can use a bolt from behind as you stated earlier w/ a short stand-off and chrome washer to the new peg!.