If you add League of Legends to Steam as a third-party shortcut, you can launch the game from big picture mode and configure the Steam Controller as usual. I'd like to move the camera smoothly with the left touchpad. I've tried assigning the arrow keys to it, but that doesn't allow for smooth scrolling and doesn't work in all 360 degrees. Does anyone know how to accomplish this?
In short, you can't. All the Steam Controller can do with Leage of Legends is send key presses that it will recognize. If League of Legends doesn't provide a 360 degree way to move the camera, then the Steam Controller can't send any key presses or mouse movements to make it do that.
If you turn on "Overlap Directions" you should be able to get at least 8 directions on the pad. Still not 360 degrees, but better than 4.