Yeah I can understand that, and if you want something ready to go like the StewMac rig, then you'd really want to be turning out a few builds. Thats why i built my own version.
The simplest one I've seen is a flat 3/4 MDF plank, with a straight rail down it on one side to rest a square against. You measure (Or lay a paper template underneath the board, line the square up and then mark each fret in turn. Once thats done you use a cut down 90 degree mitre box to make your cuts, advancing the board through from fret to fret.