While looking for a comfortable way to create some physic levels for the chipmunk wrapper i found a Cocos2D project made from Steve Weintraut that, instead of parsing the usual svg file, parses a png image and creates an heightfield based on the first non transparent pixel found in every column of the image. Then he uses this data to create a chipmunk terrain.
It perfectly fits my needs and, with very few modifications, it works in Sparrow aswell. Here there's a sample project.
-----
Edit: This script has been updated with scrolling here: http://forum.sparrow-framework.org/topic/chipmunk-wrapper-how-to-manage-side-scrolling