Adding movies to iPad thru iTunes and restoring them?

Hi,
I have an iPad 32gig. I have several videos I compress for the iPad, and rather than let the videos "live" in iTunes (tying up several gig) I found I can drag them directly into the iPad 'thru' iTunes by dragging them directly from my desktop to the iPad icon on the left side of iTunes.

They then "live" in the iPad and I can delete them from my desktop.

Good - works perfectly! BUT . . . let's say a week later, I want to restore that movie back to my MacBook Pro! I can't seem to drag them from the iPad (seen thru iTunes) back onto my desktop like I should be able to! The movie will PLAY fine thru iTunes! It's there! I just can't restore it back to my computer! Grrrr . . .
I'm hoping there's something easy I'm not doing . . . any ideas out there?

Thanks!
Larry