Yes, there is a trick. Here's how I do it:
I use the cut expansion joint on my garage floor - you know, the slot cut in the concrete. Anyway, I place the roll of tubing on the floor in the crack. Holding the cut end of the tube down, and using slight pressure on the inside of the bottom of the roll, I simply unroll it away from the cut end following the groove in the floor. Once I get enough unrolled, I cut it to the length I need. Works great.