Wow, to post in this old thread... I guess you either gave up or figured it out yourself. In the advanced options you find a button that says "import". You first copy the code from the box above into clipboard, then - I think - from clipboard to buffer. Lastly press "import".

I've got two questions on my own:
1. How do you switch from random to sorted slide show?
2. How do you keep the image to fill the entire screen?

With these questions answered, this beecon can serve as a "periodically changing wallpaper" many have been looking for, including myself.

Cheers!