This is the Mono-shock rear suspension, Right?.
It does not look like you can lengthen your straps or increase the pre-load on the rear suspension's front shock, cause you do not have a front shock. So, ... You are stuck with using the control rods or the skis' springs. Have you tried loosening the springs on the ski shocks yet?
Are you looking to have less ski pressure all the time. Or are you after less ski pressure just on acceleration? I am assuming all the time. In this case, I would start with the ski springs first.