This is going to be slow as snot.

What you need to do here is use SimilarityIndex from the diff package.  Its not public, so you'll need to either use RenameDetector, or make SimilarityIndex public.  The latter might be better.

Create a SimilarityIndex for the current origin.  Then for each path the TreeWalk is providing you, create a SimilarityIndex and score it against the origin's SimilarityIndex.  If the score is over the threshold then its common enough to consider as a candidate.