If the game detects a supported controller on startup, there is a screen before getting to the main menu where you would be prompted to press a key or button, to select the input method. After that it would be changeable in the options (or you can return to the prompt screen by hitting Esc / B button on the main menu). After starting a game or loading a save you would need to return to the main menu in order to change the input method.
You may need to use something like
x360ce to get the game to recognize the controllers.
BTW, while split screen co-op is only supported when using 2 controllers, it is the UI itelf which is the requirement, and at least in Windows you can use a virtual gamepad, like
Headsoft's VJoy Virtual Joystick Driver (with the option set to block keys, in order to stop keystrokes from also being sent to the game).
After setting up the keys, you would need to use x360ce to get the game to recognize the virtual joystick. The default settings should be fine, though opening the x360ce program can make it easier to test the key layout and assignments.
I didn't do a full gamepad configuration, just the left stick, Dpad, A/B/X/Y and start buttons, enough to see if it would work, and get local split screen going with a keyboard and Xbox 360 controller.
