Exercises to compliment extender use?

I have been using the extender for 30 days for about 40 hours total. I have also been doing 7 minutes of manual stretches (2x30sec in multiple directions).

What other exercises (other than classic jelqing) would you recommend to compliment my extender use? I started slow, but now I reached 4 hours of extender use per day, with a break every 3 days, and I want to eventually go up to 6-8 hours a day.

I am not sure if its even necessary to do something extra, or maybe its even bad? Would it be too much fatigue for my penis?