A muscle being stretched is a muscle being recruited. The old-school donkey calf raise does this very well, stretching and recruiting both major calf muscles.

1. Strap on a loaded dipping belt and stand on a block or whatever you have handy, toes on the edge.
2. Bend at the waist and do calf raises.
3. Hold the bottom stretched position for two seconds and hold the top position for at least one second, contracting hard.
4. You can perform them bilaterally (both legs) or unilaterally (one leg at a time).