I agree, it would be nice to have that feature.
I do work around it myself by hiding the tabs that I dont want the clients to see...its a bit of a pain in the proverbial, but it works just fine. I normally just let them have 'Choose Gallery', 'Add Images' and 'Manage Images' as the tabs.. I also add up at the top a link back to their PCMS installation so that they can jump back and forth easily from one to the other...
All the best