You could get the same effect with a piece of rope. Find the middle of the rope, loop it thru itself around one of the long corners then tie both tag ends to the opposite corner. Use a piece of wood in the middle to twist the two strands of rope like a tourniquet.
It probably won't take a lot of force, as you can see in the above pic the ratchet strap was still pretty slack. The weight of the ratchet was almost enough to get the job done for me.