How can I remove movies from itunes (computer hardrive) but keep those videos on my ipod touch?

So howe do i do it? I want to clear some space on my computer and keep all my movies on my ipod touch. When i go to delete myu videos on itunes, and when i connect my ipod touch, it syncs with itunes and consequently removes all my vidseos on my ipod touch. How can i work around this?