You can use an ad server such as Google Doubleclick for Publishers (DFP) Google makes DFP available for free for most websites.
By default, DFP shows AdSense ads for every slot. DFP allows targeting by demographics. You could set users from various countries to not see ads, or to see "house ads" that advertise other portions of your own site.
Unfortunately, DFP has a pretty steep learning curve. It is much harder to use than AdSense. It used different terminology for the things that AdSense does.