the shurflo backpack can stand up. Although it has its power selector on the base (yes i know, silly isn't it) you can turn it on and off by using the tap. The battery lives in a seperate compartment a bit higher up.
However, because the tap and power switch will be some distance from you, you have less flow control and therefore will use a tad more water. It works great on your back but I tend to do what Gazza does, start with it standing then put it on my back when its half full.