Cook up some real results.
The next time you set an unusually challenging group goal, up the ante a little. Announce that you will personally cook them breakfast—or barbeque them lunch, whatever is your specialty—when the goal is attained.
The key here is that you actually do the cooking. Don’t hand it off to someone else—not even upper management. It seems a small thing, but employees will go to great lengths to see their supervisor slaving away…for them. (Now, employees could help with the dishes.)