Locked into a plug harness, you say?
Hmmm
If you know any yoga, this would be a fun time to do some good deep lumbar stretches! lol
Or, an adapted yoga/meditation pose: sit with your feet flat on the floor, spine straight. Use your hands to spread your asscheeks so you're sitting ~on~ the plug and harness. Now use your pelvis to rock on the plug.
Heh.
BTW, sitting like that in general opens up your pelvis and gets you really aware of your ass, so with a plug in ought to send you to the moon and back!
Harper