IPhone :: Move Purchased Movies To Itunes Without Losing Music?

I have a iphone 4 (not S) and have purchased movies on it. Just some Pixar shorts. I want to move these purchases to my computer so they are backed up, in other words, sync the other way. I have my phone/itunes set to manually manage music and movies because my music library on my computer would be too big for the phone and I don't want all my music on my phone anyway. Problem is, I can't just drag the movies from my phone to my itunes when the phone is plugged in, and when I choose "sync movies" I get a warning box that says:Are you sure you want to sync movies? All existing songs, movies and TV shows on the iPhone "dorothy's iPhone" will be removed and replaced with movies from your iTunes library.

I want to avoid this so I don't have to take the time to reload particular songs/albums that I've already put on the phone. Isn't there a way to transfer purchases you've made on your phone onto your computer without losing everything that's already on your phone? Is there a way to sync only movies? One would think so if you just checked the box, but the words "all existing songs, movies, and TV shows" make me too nervous to check the box.