Here's something you may want to try while doing stretches or especially the rotary cranks.
Instead of pushing and pulling with your arms try leaving your gripped penis in place and putting the tension on it by moving your body/pelvis around.
Here's one of the ways I do mine: Ya gotta find something just about crotch height; table top, chair arm, cabinet, whatever ya got around.
After you're all warmed up and ready to go, go on over to the table top, let's say, and using whatever grip you prefer for the exercise in question, grip your penis good and hard and then place it on the table top.
Then use your legs to move up, down, sideways, back and forth. Use your pelvis to twist and rotate around (think Elvis, maybe).
Instead of pushing down with your hand do a "crunch" or pelvic thrust to pull the root of your penis up. Think of all the motions you might use during some good ol' athletic sex, or some really raunchy dancin'.
Experiment with this a little and you'll find that you can target from tip to root and even your inner penis just by paying a little attention to the feel of each movement.
Standing up also stimulates the bloodflow throughout your lower body, builds your [words=http://fleshlight.sjv.io/c/348327/302851/4702]stamina[/words] a little and even helps your imagination through building muscle memory.
That'll help ya last longer in the sack !
Hey, if anybody tries this and it works for them too; let us all in on yer progress!
Good luck with it.