I did this when working through a knee injury. Moved my treadmill to a part of the basement where the joints were exposed with the treadmill perpendicular to the joists. Bought the Lever shorts and 50' roll of 1/2 bungee off Amazon. Went to Home Depot and bought 4 C-clamps. 2 C-clamps on the joist at the front treadmill about TM width. Hung full body weight from the 2 C-clamps to test weight bearing. Ok. 2 C-clamps on the joist at the back of the treadmill. Tested weight bearing. Ran bungee like Lever through shorts. Used a Grigri (rock climbing belay device I had) to adjust tension from front right corner. Home Depot probably has something similar. Have to slack it quite a bit to get into shorts, then tighten with the grigri. Checked tension with home scale at first, but later just went by feel. Later added pulley in the back to even tension. Grigri slips slowly and I adjust on the fly with right hand but it works.