Can you use the green screen effect with the iMovie app using the iPad 2???

I was wondering if I can use the green screen effect on iMovie using the iPad 2 like you can do it on iMovie on a mac laptop?? The way you do it on a Mac laptop is by dragging one video on top of another but it dosent do that gesture on the iPad 2 iMovie maybe it's not possible on the iMovie for iPad 2 but it would be great if someone knew how to do thee green screen effect on the iPad 2 iMovie !!!