what i do now i really like.
2 sets standing calf raises. Very heavy 8-10 reps, i actually do them with a slight bend in the knees, nothng major but going very heavy with locked knees can sometimes hurt.
2 sets toe presses on leg press. If you can, do these with your shoes off. Feels WAY better barefoot than with shoes on. 10-15 reps. Also, after each set i straight away stand on a block of wood and hold the stretch for a minute. The pain is crazy, but i have noticed an improvement since implementing this extreme stretching. Awesome pump.
I wouldn't do this stretching with any other muscle group, but calves seem tough enough to handle it.