I found an app that can reset the inactivity timer for games like Clash of Clans and Boom Beach.
As an example for Clash of Clans, normally the game brings up an inactivity timeout message after about 4 minutes of inactivity . This simple app briefly takes the game, puts it in the background and then bring it back to the foreground. This has an effect of resetting the timeout clock. The app launches a service which can be paused/exited from the notification window. Now since the app keeps the screen on, it can be battery intensive, but, for the case of Clash of Clans it really helps to protect your loot in between building troops for farming.... On the google play store it's called AppCycle Pro -- check it out, leave feedback, share requests for improvements.
The app is general purpose, you can select which apps to cycle, and set the delay for how long it keeps the app active before cycling it.
I'm sure there are plenty of other games that would benefit from keeping the game active.