How to set up popunders chain?

Hi,
I am considering using adversal as a backup to paypopaup popunders when paypopup has no ad inventory to show. What is the best way to do it technically?
In my paypopup account I can see an option to specify a default page URL to show up when there are no ads to serve, but that has to be a URL, while what adversal provides me is a javascript code snippet.
Thanks,
mkassets

Original post by mkassets