Midi Console Add and Subtrace Functions

[TecAlpha]

Is there a way to make a fader on a midi console add and subtract a specific channel, add if the fader is above half, subtract if it is below half? This would make it so that the fader would do nothing, add to the current value if you push it up, and slowly subtract as you push it down, so it lets you "tweak" the current value. I have tried with no luck so far.

Thanks,
T.J.