Backing up apps that are no longer available?

I did a search on backing up apps, and from what I gathered, there are ways to back up the entire library pretty easily.

What I'm curious about is whether it is possible to back up select apps by dragging them into an external, and later dragging them back to iTunes in a new library. I don't mind losing the music playlists and other metadata but not the apps. I want to format my hard drive but I don't want to lose the apps that are no longer available on the App Store.

Nermal said:

Works fine. You can drag and drop .ipa files into iTunes just like a music or video file and they'll copy across to your iDevice.

Click to expand...

Just what I wanted to hear. Thanks.