I don't think you can directly reuse subobbjects. I don't see a way to copy or move them to other master objects.
On the other hand if you XOG them out with the parent and edit the file you might be able to XOG the file back and create similar subobject for another master object.
A small error in doing that could make your system nonusable.
Secondly the xml files which include master and sub and views tend to be large and cause out of memory issues.