3rd spring questions

[Rizzle]

So,
I'm designing a 2wd short course truck in my extra time while at school. I figure its a good way to get some CAD time/hands on formula use and plan to build it in a couple years with a buddy of mine.
Now, I have a decent understanding of why they use a 3rd spring on track cars with high sprung aero loads, to allow softer ride rates without bottoming out at high speed. I *think* that the short course/desert trucks have a situation where the opposite would be beneficial, due to high amounts of travel and soft spring rates and I'd like to see if I'm on the right track before proceeding with it.
I'm thinking that instead of using a third spring to add spring rate, it is used as a negative spring, either on the center of the rear axle (solid axle this time - simpler - easier - cheaper) or the center of the roll bar (front). This would allow for stiffer wheel springs to control roll and maintain a softer spring rate to get maximum travel when landing jumps.
The downside I see is single wheel bumps upsetting the suspension if the wheel rates end up being too high.