Pretty much by definition, modified files are not tracked. (Uncommitted modifications are, well, uncommitted.) You could certainly directly copy the work tree if you had access, but otherwise, if you want to pull it, you need to commit it. You could commit it to a temporary branch, of course, but somehow it's got to be committed.
Edit: This answer is about pulling with git. If you want to copy files (or copy a diff) as in the OP's answer, you can do that, but the bottom line is that it's an operation requiring filesystem access, not a git remote operation.