I do a full body circuit workout when I'm on my treadmill:
5 min TM warm up
then place feet on sides of TM and do 20 squats,
While still in squat position, place hands on center handrail and pull body up using biceps (bicep curls) x 20
using handrails--20 standing push ups,
using handrails, bend down so that butt is touching the top of the TM belt and both hands are on the center handrail and do 10 pull-ups
using one side of handrails, do 15 tricep dips
5-10 min TM
repeat above sequence
etc.
Typing fast, sorry if my description doesn't make sense. The idea is that you don't have to get off the TM for the entire workout.