Technically, exhaustion is already factored in, sort of. The more Gs you pull, the more likely you are to fully black out. That is, if you pull Gs and "ride the tunnel" then ease up, then do it again before the fatigue has worn off, the next time might black out out faster, and for longer (perma-blackout). HTC mentioned this once long ago.
Not what you were thinking of, but still better than nothing, eh?