I've been using ControllerMate to approximate a response curve for my joystick with reasonably good results. There may be a simpler way but this does work. You will need to setup and use a Virtual Joystick for the axes you wish to work with (VO handles multiple joysticks well). The actual input and output numbers are listed in the note attached to the primary input block. The values listed result in an output curve as shown in the last screenshot.

I omitted the Y-axis since it is uses the exact same values as the X-axis with Y-axis Input and Output blocks. I included the R-axis since it uses the same curve to map an input range of 0-255 to an output range of 0-4095.

Also, in the lower-right corner of the screenshot for the X-axis is how I mapped a digital control to an analog output which VO recognizes.

X-Axis

http://img87.imageshack.us/my.php?image=controllermatexaxisfk1.png

R-Axis

http://img513.imageshack.us/my.php?image=controllermateraxisbv3.png
Input/Output

http://img504.imageshack.us/my.php?image=outtd6.png

P.S. Recently used ControllerMate to add some auditory feedback to a few buttons - surprisingly easy to do (just attach a sound output block to a button block, the button continues to function as normal otherwise) and very helpful for confirming the toggling of functions given the lack of any other feedback. (I use the echo command for feedback for my custom aliases but it's easy to miss in the chat box if things are busy - the sounds are immediate and visceral.)

Very nice! I tip my hat to you, good sir.