Quote Originally Posted by Colin500 View Post
It's just a shortcut that, for every click of one wheel in one direction, automatically does a click of the other wheel in the other direction, so that you keep the same exposure...
That sounds an awful lot like...P Mode. In P mode, rotating the main dial reciprocally adjusts shutter speed and aperture.

You could assign mode change to M.Fn, and restrict modes to just M and P, and that would get you there (as a 'bonus' you get EC with the quick dial in P).