Algodoo

...This is also genius...

I don't think it'll be able to lift my madcat, though... But you could always try to make an uber heavy duty one! OR is it still in the making?

I gave tweaking instructions for a reason.

I decided to go for power, and managed too tweak it to lift 300kg without scaling anything or changing density. I think it'll need scaling down for your madcat, but I checked and it weighs something like 25kg. You may need to do some text edits to get it to work for you.
If the large spring has to be so strong that the movable wheel can no longer turn the free wheel, try increasing the friction between them and/or increasing the power of the wheel that pushes the piston.

And if you have any weight problems with your vehicle, you can also leave the large spring under tension (reduce its target length) and it will constantly pull up, and give an extra pull when you engage the jump.

I'll uhh... Think... And keep thinking, so that I may possibly figure out how to get this to work... I'm only used to traditional methods of power... never seen anything like this in Phun before, I don't know how to work with it.

The red and blue circles with the springs are the heart of this system. you can make a simple mechanism to yank on it with a spring to make it move. it goes in the direction opposite of the pulling.

if it could be possible with a peaceullier-lipkin linkage.... it owuld be more stable. or even if if the rotating joint moves a piston...