Here are the instructions for the soda can fix method. I doubt that a glue gun would last since there is so little surface to stick to (and you need to pretension the rod a couple twists so that the roller will retract all the way)...but it depends on how yours broke. Mine had very little surface left so I added the metal piece.
If at all possible, use some slightly heavier metal than the can, but mine has worked for 6 months so far.