Talked to the factory, they said not only would I have the cross flow problem, but also the PB valve would leak! So much for that idea.
Asked them about putting a thermostatic valve in to feed the hot side of the pressure balancing valve, (teeing the cold to go to both). Basically using it as a hot water limit. Then I could turn the PB valve full hot or off, and get the same results. They didn't even want to go there!
They explained that any pressure drop caused by the first valve, would cause the second to match it on the cold side. So how much pressure drop would a 1/2" thermostatic valve produce? Enough to choke the hot/cold water supply coming out of the PB to cause a problem?
Sounding like it isn't going to be worth the trouble.