How do I prevent apps from blocking a second screen? I used Google cast to cast my phone's screen. That worked. But all4, the Channel 4 catch-up app, wouldn't display on the second screen. A message popped up saying "all 4 doesn't work on secondary screens". How can i stop the app from detecting this? I'm rooted and xposed, s5 touchwiz lollipop
Try xPrivacy.

You might be able to limit the permissions of the all4 application you mentioned in such a way that it cannot tell if Google cast is running.

The Github page has the full options on what is available.