I don't think there is a way to not export all the photos. Pretty much any of these types of programs use some sort of proprietary database software to index all your photos so that they can come up quickly and make them even easier to edit and automatically save. When you want to switch program you basically have to flatten your stack and export all your edits. With that said, if you are worried about time, I do not think it is a very long process.

I would echo the above posters Picasa suggestion, though personally I would go with Photoshop Elements if you are willing to spend a little money. I think it is less than 100. It has a stronger photo editing backbone as well as, in my opinion, a much better tagging and sorting set-up.