Since the lower leg muscles are relatively small, you can work the entire muscle from origin to insertion in just a few minutes. Here are a few options for every part of the calf musculature.
Extend the knee and bring your toes back toward you. Center the roller on the muscle and use the opposite leg to add pressure. Use only 1-2 inches of back and forth movement, 30-60 seconds per side.
The knee must be fully extended to hit this area of the calf. Internally rotate the leg and pull the toes back toward you.
Externally rotate the leg for this one.