I have disabled the Android back button:
https://forum.mendix.com/link/questions/91003
(Just making sure others get to know how to do this when they see this post)
Hey Mark!
I think you'll need to write some custom javascript to alter the back button behavior. Check out these documentation pages:
https://cordova.apache.org/docs/en/1.5.0/phonegap/events/events.backbutton.html/
https://www.npmjs.com/package/cordova-plugin-backbutton
The one on npmjs you could wrap in a widget or html/js snippet and write your custom logic for.