I was able to follow the typemap suggestion, adding a mapping that eliminates most cases of the repeated code I wanted to avoid. It's slightly nefarious, since I'm sneaking around the back of the smart pointer, accessing the underlying pointer directly, but I think it's justified within these internals.
in reply to Using XS To Wrap A C++ Smart Pointer
An issue I didn't mention in the original post was that the smart pointers were pointing at objects belonging to a large class hierarchy. I'm using boost::shared_ptr for this, since it provides nice support for implicit conversions from smart pointers to derived classes, to smart pointers to their base classes. Dealing with this in the XS required writing a small class hierarchy that wraps these smart pointers, but restores the original class hierarchy that the smart pointers concealed.
Thanks for the help.