I am using Dozer to map between a Document class to DocumentManagementBean class, both of my own making. Both have a property, with getters and setters, of Joda DateTime type, c
You probably don't need it anymore, but Dozer provides the chance to copy an object by reference, at least with the latest version (now, this version is 5.4.0). Copying by reference is what you are looking for.
copyByReference
copyByReferencePrime
Documentation: http://dozer.sourceforge.net/documentation/copybyreference.html