I don't think there's a mod out for this (though I've been wrong plenty of times before ;) )
Does your gamepad come with a mapping program? I have a Gravis Exterminator® (
http://www.gravis.com/products/pro_xte_d1080.html) Gamepad for the pc that came with the drivers and a handy little Keyboard mapping program. It let's me assign Keyboard combinations to the many...many buttons, plus it let's me assign the custom keyboard combos to a particular program so I can map different sets for different games.
GameSets: Program different button and axis settings for each game. Xperience will automatically detect which game is running and load the correct GameSet.
Keyboard Emulation: Assign any button, POV direction or D-pad direction to send a keystroke or key sequence to your game. Primarily for pre-DirectX games, but also useful for programming one button to perform a series of actions.
Axis Control: Choose Between "Joystick", "GamePad", "Keystroke", or "Mouse" mode for each joystick and proportional D-pad, and also adjust their Null Zone, Sensitivity, and Acceleration.
Axis Swapping: For devices with more than one proportional control, choose which axes are assigned to each control: X-Y, U-V, or R-Z.
I haven't used a gamepad in ages, the one I have is a different & older version from the link above (I like mine better), but I would hope some of the newer gamepads have a similiar function? (My gravis pad is several years old, but still works whenever need be)....
Try checking your gamepad's manufacturer site to see if they have such a beast