My friend saw a similar thing somewhere and wanted one for himself, so I made him one. Tried to make it as compact and functional as I could.
Fits all my fly reels ranging from #2-#7. Have not tried any other reels, but I suppose scaling will do the trick if your reel does not fit.
Tape, glue or screw in place.
If you need to re-spool your reel, I also have a Fly Line Spooler: