Time Machine (avoiding unnecessary complete backups)

So if I want to move a user directory onto a different drive from my boot drive, and have time machine set to back up that second drive, it's going to treat that version of the user folder as different files, and trigger a fresh complete backup of them, thus eating a huge hunk of my time machine drive's history.

Does anyone happen to know if TM behaves differently if the folder is recovered from within time machine to the second drive? Does that cause time machine to see it as an extension of the previously backed up files, so it only gets incrementally backed up on subsequent changes?

Or, does anyone know of a utility that allows you to manually link folders so you can control the continuity of backups when sources move?