I have experimented with using HDPE in a similar manner to that described for clipping in aluminium tubes in folding kayaks like this http://www.yostwerks.com/HDPE0.html with some success. All you need is a small piece, maybe 5 cm by 7 cm and drill it at the correct angles to match your fork and rear seat stay. You drill a hole that is the diameter of the tube but offset it so that the hole is only partially on the piece of HDPE which allows it to snap on and off the tube. Works pretty well on a single tube, but for multiple tubes you need a pivot with a hole on each piece or measure the angles that the fork and seatstay are at and then drill the HDPE accordingly.

For those who aren't familiar with HDPE it is the plastic often used for cutting boards.

I just use Velcro one-wrap on my folders because it is bombproof and cheap.