I thought you might be interested. Someone else--perhaps I--might eventually do it if you don't feel like it.
It occurs to me that this comment there is misleading. Taken literally, they are technically saying that prename should be used and not file-rename, but they probably mean (or would prefer to mean) that either of them should be used instead of rename.ul.
Yeah... though prename would probably be okay too.
Unless you recursively enumerate the paths and assign them to @ARGV in a BEGIN block instead of using find or globstar or something. BEGIN blocks don't seem to work right with prename.