If you're playing the PC version and you're watching the video I saw then you can't do it that way. Apparently when you change forms in the PS3 version you get a little extra upward boost, but not in the PC version. I had to start out a screen or two to the right and do a bunch of climbing and bouncing.
Gorfinhofin is right that the pc version does not have an extra boost...
but if you try harder you can bounce on the slopy roof which will allow you to reach extra height and can than reach the first spot.
It works by converting your horizontal speed into vertical one when you bounce on the slope... :-) . you will need it in 1 or 2 other achievements...
If I remember correctly, I got that Achievement another way.
I got the green power-up on the far left, then bounced to the right as far as I could go, and used it to fly to one of the walls that are high enough to allow me to bounce my way to the Achievement.
Here's the video. (http://www.youtube.com/watch?v=TCtzDZnbNmQ)
I can't tell if it's easier this way.