I can't stand on the trainer, either, Blueberry. If I do, it has to be in the hardest gear, and then it kills my knees. While I find it takes much more energy and slows me down on the road, I can stand. I also see people looking so natural when they stand; not me.
I don't like the elliptical for this reason. When the resistance is hard enough, it hurts my knees.