I've read the same book and this is what I did.
I went to a level sports field or near one that wouldn't bother anyone and walked off yardages and put towels at 40, 50, 60, 70 & 80.
Use all your wedges at 7:30, 9 and 10:30 and make your best estimation at their averages (or if you are really anal, right them all down; or get your kid to do it...what else are they doing that's productive?)
Note where they land, not where they roll out. Discard mishits and any shot that just didn't feel right.
Definitely make that label he suggests at the base of the club with the 3 yardages for each position. Very handy on the course.
The "rolling out" part will have to be determine more from experience. Obviously a PW is going to roll out more than a LW. So experiment on your home course and note how those shots roll out. You want to pick the landing spot on the green and estimate the roll out based on the club you picked. PW will need a landing spot farther from the hole than a LW.
One last thing, as you get better at making the shot (you are practicing it right on the range right?), you'll probably notice your distances change. For me, my rhythm changed and made my shots go farther. I recommend after 6 months "recalibrating" with another "towel session".
I think that part of his book was the most useful for me and definitely improved my scores.
Good luck!