Use one leg for this leg press, but keep the other foot on the platform for safety, I lower the safety foot and raise my heel up so that I am not tempted to put weight here. Make sure you start lower weight that what you would normally use to avoid injury and practice proper form here.

Weight Recommendations:

Beginner: 5-10lb plates on each side
Intermediate: 20-40lb plates on each side
Advanced: 45-90+ lb plates on each side