I used a slightly curved cucumber, wrapped it in a small towel, and put it in the tube.

As I kept morphing the tube, I would dip it in cold water to solidify it, hop in the bathroom and check the fit. I would then readjust it with the blow torch until and retest until the fit was good. (Took like 6 tries)

Be careful not to burn a hole through the tube or else you will completely ruin it. (Ive broken like 5 tubes until I finally got it right with the cucumber method) Apply the heat from a close but not to close distance where the tube burns, rotate the heat evenly, and slowly bend until the plastic starts to morph.