Google-friendly is usually means native, at the moment setting pop as tabunder on click by thumb or on internal links has already helped to pass google check for many webmasters.
To set this behaviour go to websites, find your website and popunder spot you want to adjust and click edit button.
Select tabunder and Bind to: your thumb element class
Your visitors will get tabunder only on click on the thumbs and nowhere else.
If you don't know the class of your thumb elements use developer mode in your browser to find it.
select element picker
Point your thumb
find class name in console
Look an example below:
You may use these settings for all browsers or only for Chrome, in this case add targeted config for Chrome browser in the right panel:
Also read the full manual of popunder settings or ask us on chat in case of any problem.