Actually its in book 1. Re-reading everthing carefully in prep for the Nov Instructors camp.
To paraphrase from memory - while the wedge is not used as any step in a progression - we teach it as LMD or "Lift(line) Manuvering Device".
And you know what - that's about the only place where it would ever have any point. Two narrow to side slip, tad too steep for poles.
Actually I was at a PSIA taught race camp this summer and I didn't see anyone using the wedge in lift lines. Poles work fine in 99.99 percent of cases. And, these were not PMTS people either. They are just skiers that race that don't like wedging for most any purpose. Why would anyone, it's pretty uncomfortable.
Where a lot of people would use a wedge in a non-race envirnoment at most resorts for lift line approach, etc, these skiers just did partial side slips (not 90 degrees in other words) to slow down.
I think that may be the only reference in any of HH's 3 books that says PMTS includes a wedge in any way shape or form as a tool of PMTS. (lots of drills to help people undo the wedge of course)