Been hunting the same thing myself. All I've been able to find is a simple data on/off toggle widget.
LTE is a battery hog. Love the speed, but don't need it to just sit in LTE mode while my Xoom is just idling. Having to go into settings and change it back and forth has become a PITA, so I just use the data toggle widget and leave data off when I'm not using the Xoom.