Moved to Suggestions, redirect link left.
I was going to ask why you would want to play this game one-handed, but I don't Think I want to know...
But to be a bit serious, my phone has a back button in the bottom left corner and I use it all the time and it's quite convenient. I Always get a bit annoyed when I play on my son's phone and there is no back button down there. Yes, I play the game onehanded a lot, and I do all sorts of things with the other hand.