Here are some uses I have found for using my old strings:
I used them for cutting cheese. They also are the best cutter for homemade soap, whether you bake it yourself, or buy a large soap loaf.
You can also use them for cutting rolls of cookies or cinnamon.
To make the strings safe without hurting fingers, my husband secured them to wooden dowels.
There should definitely be a place to mail your old and broken strings to set up by guitar string manufacturers. As a musician I'm very bothered by much of the ethics of guitar manufacturers in general, but this one is a biggie.
A really simple use too is the old fashioned pick necklace. You put a hole into an old pick, use an E string and slide it through the pick. I had mine for a while.
I cut them into 10 inch pieces ( tops and bottoms ), then stick them into a wine bottle CORK.
Hotglue the flat end of the cork to an old CD..
Hotglue a couple of guitar picks together so they look like butterflys and then hotglue those to any of the strings..
Makes a beautiful center piece, especially when the sun hits it..