Just rotate the powerjelq if you want to hit the sides of your penis. (that is turn the device a quarter turn clockwise, put the rollers on the sides of your dick)
There is a built your own jelq device thread somewhere.
ON EDIT: Here is is:
Homemade Power Jelq, a Jelq Device
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Also see number 2 regarding how to use on the sides of your penis:
Jelq Sticks
Power Jelq
1. Warm up, apply lubrication, and achieve the appropriate level of erection.
2.Hold the device with one hand on the two handles, palm facing the body. If using the device horizontally (i.e. on the top and bottom of the shaft), use the other hand to grasp the foam rollers. If using the device vertically (i.e. on the sides of the shaft), use the other hand to hold the base of the shaft. This will prevent slippage and/or twisting of the penis during the exercise.
3.Open the handles and allow the rollers to slide onto the shaft. Push the device all the way to the pubic bone and then push a little farther, lightly squeezing the handles. This will pull the penis out of the body slightly and begin to force blood into the shaft. Alternatively, a light OK grip can be applied to the base, holding back loose skin and slowing down return blood flow.
4. Close the handles, gripping down firmly and begin to pull out and away from the body, up the penile shaft and toward the glans, concentrating on trapping and moving blood through the shaft. The grip should be tight enough that the rollers lock up, and only turn very slightly (if at all) when pulling upwards toward the glans.
5. The stroke should end an inch or so below the base of the glans. If performed correctly, the glans should be so engorged that the device cannot slide off the shaft without the grip being loosened.
6. Loosen the grip on the handles, sliding the rollers to the base of the shaft and repeat for the desired number of repetitions.