You can change the controls in the options menu - even the hidden key bindings can be re-assigned there (although, this can make navigating the UI tricky if you lose all movement options). Set left/right/up/down to the dpad, and then you just have to choose something else for equipment/inventory/quests.

If you're using Xpadder, then just make sure all gamepad inputs are mapped to the keyboard - as any gamepad input will switch it back. I think steam input can also map multiple gamepad inputs to the same output in game (and even allow for button combinations).