Have you tried emailing coach sommers about this? He is fairly quick about responding to inquiries.
George, though this is an old thread, most of the book touches on laying a foundation of leg strength. I'm sure there will be more interesting drills when it comes to the book on dynamic strength ( which is no.5[?])
For doing a basic front tuck salto on floor, most of the girl's only have a vertical of about 12-15" which is roughly 20-25% of their height. Nothing impressive. Even the girls doing a back tuck out of connected back handsprings ( with good form, not cheer form ) are probably around this 20-25% ratio and it only takes about that much vertical to do a standing back flip.
Same goes for the boys who have similar skills.
I'm pretty sure Charlie Tamayo ( who is very close to a standing double back ) has a pretty insane vert height. He can actually do it if he lands in a mat in pit. I've only heard of a handful of people being able to do this.
You don't need a lot of leg strength unless you're doing some monster vaulting or tumbling and the finer technique you have, the less power you need unless you're doing double fronts off vault or triple backs on floor.