I used to think this was a one way level, [down only] but I figured out a way to get back up. First, you should master the high jump. Jump twice, and on the third jump double tap the space bar. Once you can high jump on command, get some lettuce edit: spinach and activate it mid second jump. The third jump will launch you all the way to the to the very top.
Here's proof:
http://www.youtube.com/watch?v=LRMUWMd8Png