I like that mental image of jogging on one wheel. I took the 29er out today around the campus and experiment station and focused on pretending I was running down the road. It felt to me like like this resulted in a more upright posture with my butt under me a bit more. I even imagined for a while that that when I got it right, it resulted in less effort, although that was probably just wishful thinking.
I also noticed that as I fatigued, I had more difficulty with both that mental image and with my posture. As I got tired I tended to slump over.
The dude who writes the Muni or Bust blog recently commented on how his lower back was aching after riding in a couple of mountain bike races. Firstly, good on him for riding in those races, but I wonder whether the strain and fatigue of that riding causes him to slump forward (he alluded to that in a post) and puts pressure on his lower back. I'm certainly in no position to give him advice - he's racing and I'm just wishing - but I'm going to keep on with this mental image and see if it results in less fatigue over distance.
There is at least one problem though...my upright body seems to catch a lot of air. That's a problem on some legs of my ride because the winds whipping through the midwest can provide a sustained pressure that feels to my legs like a challenging uphill climb. I've been knocked off the unicycle more than once by the winds I encounter riding the lanes through the experiment station. Today those winds were blowing and when they hit me the jogging image instantly vaporized. I was reduced to using whatever body angles and motions I could to stay on top, including slumping, swerving and jerking in a very unjoggingly manner. Tough. Maybe jogging is just my fairweather friend.