It is pretty much impossible not to drop the back shoulder some. If the back shoulder doesn't drop, the hands have to roll over.
We are seeing some progress with my son. Removed as many moving parts as we could from the swing, shortened his load and had him start wider so that his stride is "shorter". He still has a few tweaks to make, but is making much more consistent contact. In doing that he did seem to sacrifice some power, so we will have to see over a longer period how that works out.
Thanks again for all the suggestions, some of these were really helpful in pointing out what we need to look for. I will post video soon, after I recover my failed hard drive.