I'm not convinced it's possible to do real sprints on a treadmill. Even with my short little legs, I doubt that it has the room for me to break into a full running stride.
Doesn't your gym have a real gymnasium/basketball court? If so, run from one side to the middle and back, then to the far wall and back. I've never timed it, but I'm pretty sure it's less than half a minute, and there's no way I can keep up that pace for a full minute. I gasp for air for about a minute, then I do it again, usually four times, interspersed with push-ups.
It is easy to get lazy with it when you're by yourself, which is why I always nab somebody standing around the weight room to do it with me.