How to sort folders for desktop wallpaper?

I'm not asking about folders on the actual desktop. I'm talking about:
system preferences ->Desktop & Screensaver ->Desktop

A pane on the left allows me to add folders of images that I can use as wallpaper. The folders are displayed in the order created. I'd like to sort them other ways and I don't see any way to do that. Yes, I could delete them all and then add them again in the desired order but I'd have to redo that every time I add a new one. Any suggestions?