Firstly, cut the tie in half. You'll need the bottom half.
Fold the square end of the tie, leaving the end to be used as a little flap. Sew up either side. Remember to leave an opening for your pouch.
Sew a button onto this part.
Cut a little button hole into the top flap and sew around the edges of it.
Voila! You now have a lovely small pouch!
(Sorry for lack of pictures!)