Start in big ring, easiest gear. Spend 3' in each gear gradually working your way to hardest gear (total 27').
Leaving it in big ring, hardest gear, do a 10' TT. Go small ring, middle gear for 5' spinning smoothly. Go back to big ring, hardest gear, and do another 10' TT. Gradually work your back to your easiest gear by 1' for cool-down.