That was actually my initial plan.  The problem was that I couldn't work out a simple solution for consistently locating the rail at a specific angle and offset from the vertical rear edge for 4 sets of holes.  I'm sure I could have made it work, but it started feeling much more fussy than a simple bushing-style drilling template.  The Festool LR32 system just wasn't designed to drill shelf pins at an angle (off vertical) while still keeping the shelves parallel to the ground.