An easy way to increase the eccentric (negative) loading is to do the concentric or lifting part of the rep with both legs, then the lowering part with one leg. After you hit failure with the single-leg eccentrics, continue the set by using both legs and a controlled negative.
Alternate legs on each rep. Make sure to do the eccentric portion in a controlled fashion to take advantage of the overloading effect. Don't just let your leg freefall when lowering the weight. Do 4 sets of 8 reps.
A while back here at T-Nation, I released a series on what I called Pendulum Training. This is basically a training system that has you switching from structural training to functional training every week.
Stimulants can really get you amped up for a tough workout, but do they have other effects as well? Dr. Lowery hooked himself up to fancy lab equipment to find out.