All WCS employees have motorized sit/stand desks that can be adjusted up or down. But even before we had this fancy equipment, people found ways to stand while working. Walking meetings were popular, of course, but I also remember seeing cardboard boxes and reams of copy paper propped under monitors and keyboards. Sometimes you have to get creative!
If you've been sitting for too long and need a break, check out Dr. Frank Lipman's "Desk Dweller's Repair Plan". He recommends several great stretches that can help ease tension and pain.