Build an array of light bricks 5 tall by ?? and use slopes or pins attached to the tread to activate the lights as they pass.
Very cool idea! A wind-up jewelry box operates on a similar principle.
https://www.youtube.com/watch?v=uIrlTpl1uJY
Do you think the lights could be placed close enough together to appear to spell something? Would there need to be some kind of diffuser to make the light less intense and spread out over the entire space between the individual light beams?