This instructable shows how to hack your Mechamo Inchworm to make it crawl along a suspended string. It's surprisingly easy, and should take about 10 minutes!
Here's a video of my hacked Inchworm cruising along upside down, suspended from some nylon string:
But how does the inchworm normally work? This article has a general overview, and the video below is a good example of normal operation.
Get your self a nice little rubber band. Mine is one of those teal ones they wrap around your eggs when you checkout of Whole Foods.
Get a metal coathangar, and cut two pieces about 10" long. Ben them into Ws as show. Make the outside arms of the W about 2 inches long, and the inside arms ( the upside down V part) about 3 inches long. When you suspend your inchworm from the string, this will position the string right between the bottom of the inchworm's two feet.