I had to design a small serie of USB for a design conference in Montreal and here was one of my concepts.
Step 1: Iron + adhesive veneer
First, remove the plastic shell of your old USB.
Cut the shape you want in the adhesive veneer sheet.
Put the USB drive in between the two sheets. Sticky sides facing the pc-board.
Iron the edges until the merge.
Repeat for the cap.
Sand down the excess glue and wood for a sharp edge.
You are done!