Look, I've redone this twice and none of the platforms move. I always kill the beamos and rats.
[Youtube]
http://www.youtube.com/watch?v=QYoC1z_5jMQ&feature=channel_video_title
[/youtube]
Look at 4:09.
[Youtube]
http://www.youtube.com/watch?v=QYoC1z_5jMQ&feature=channel_video_title
[/youtube]
Look at 4:09.