When doing a diff between two paths in a repository (say, /trunk/... and /branches/...) remotely (referencing a URL instead of on the local filesystem), extra information appears in the headers specifying the path the file resides in along with the revision. We didn't parse this, but it's easy to add.

Normal diffs upload fine.

Uploading a diff generated by:
  $ svn diff http://svn.example.com/trunk/foo http://svn.example.com/branches/foo/bar

now works.