How to display Featured First & Random and then non-featured also random?

WP 4.1 DT: 8

Hi,

When we click on any of the categories the systems takes you to the category and display all listings relative to said category. It displays Featured and non-featured as well.

We tried going to General Setup>Search/Listing Page > Display Order.
The select pulldown menu does not contains what we need.

If we choose Featured: all non-featured will not be shown.
The random option does not exists.

What we need is a behaviour similar to the following query but that all displays Non-Featured randomly after Featured listings:

meta_key=featured&meta_value=yes&orderby=rand (this displays Featured only random)

Said query works well in the HomePage in Page Setup>HomePage>Display Setup

How can we add a query to the categories area so that when a user clicks on any of the categories the systems takes you to the category and display all listings Featured First & Random and after that Non-Featured also random?

Why we need this? We want to be fair with all advertisers and provide the same amount of advertising according to their investment. Its seems to be unfair that if an advertiser paid to be listed as Featured, non-featured will be shown first. On the other hand, it also seems to be unfair that if a non-featured paid to be listed, it is always be displayed in the same position within the non-featured group. Random display within every group: Featured and Non-Featured its fair.

Please help.
Thanks in advance!