What I do is in a 100% erect state, using plenty of baby powder and gripping with the standard ok grip (the one I use Still, I think it is different then yours from the pictures you sent me) I stretch doen and out against slightly against my erection angle. I do these straight down, down to the left and down to the right. Another variation on these that is excellent are Clock Bends on the MoS Site.
Its simple. Do the clock bends like DLD mentioned.....get erect penis and bend it left than right going all the way up the thing. Hold the stretch for 30 secs or so. I did this....it stretches the whole one side of the CC.
Also theirs the Erect Tunicae stretch , simply grip around the head....it may hurt some...it dunt me. And pull the erect cocker towards ya chin,,,,so ya target the tunicae. Put a little bend in it,,,to put more pressure into the stretching angle. I do a Constrictorized Tunicae stretch ....it is great. Do a constrictor at fully erect and than do as I mentioned....it stretches the whole maximum erect penis.