I've got to "5th" harleybob's way of adding any backing and line to a reel. And, I also use my "Reel-E Good" line winder to do it too! It's the neatest, quickest, easiest, way to handle any "fly line job" I've ever found. With the extra spools, (like A-Grayling mentioned), it's a fantastic tool for doing backing, cleaning and dressing fly lines. Mine is around 5 years old but even "being made of all plastic" it's still as good as new.
I also made my own adapter to chuck into my cordless, variable speed, screw gun to use on the reel, and/or, on the large take up spools and can really do a lot of line work in a very short time!