I don't think it's possible. This game wasn't really designed for mouse & keyboard control. If you try to force it, you're bound to encounter all sorts of issues that will make your gameplay feel unnatural. Instead of trying to get around them, you're much better off acquainting yourself with the default keyboard setup. After an hour it will feel natural enough, and the horrible aiming along the Y-axis or in the sniper mode isn't a big deal anyway, there aren't too many situations when enemies are above or below you and you can't lock on to them with autolock.