There is a technique available like the one you describe. You know, that's exactly how published QVW documents with server objects behave. Server Objects are personalized objects that belong to the user that created them in the AP or imported them from the Repo. The underlying document can be changed at will by the developer, without affecting the Server Objects as long as the developer respects the data model requirements of those Server Objects.
But if you are talking about two QVWs sharing common objects, then I think you're out of luck. There is no Object Library feature (yet) in QlikView...
I'm not sure this will work, but you can try a workaround by exporting your two documents to a -prj folder. If the common objects share the same IDs, their xml exports will have the same file names. If you now change some feature of a common object in the standard document and store it in the -prj folder, you could pick up the xml object export and drop it into the -prj folder of the second document...
