Step 1: Materials
a florist's water vial. I asked for a few of these at my local flower shop and she sold them to me for 25 cents a piece. Try to find thin ones as they will be easier to find heat shrink tubing to fit.
heat shrink tubing that will fit around the circumference of the tube. In my case I needed some at least 3/4" wide.
a heat source such as a propane torch or a heat gun or hair dryer
Step 2: Assemble
carefully insert the non-writing end of the pen into the remaining heat shrink tubing
use a hairdryer or low flame heat source to slowly and carefully shrink the tubing around the pen until it conforms to the shape of the pen and holds it snugly.. Be careful about heat: keep your fingers and hair away and don't burn yourself. If the heat is gentle enough, the pen will remain functional