Post-processing does this for free.
Shoot RAW, post-process. If done correctly, the result will look very natural.
I'm also not surprised that you haven't found a more contrasty lens than the Zeiss. I don't see anyone raving about Canon colors compared to say, Zeiss or Leica colors. Perhaps I'm not looking close enough. I'd guess the latter.
Honestly, there's only so much a lens can do. When you reach 100% light transmission (I wouldn't be surprised if the Zeiss got close), then from there it's either the sensor that has to capture more color information, or you fix the perceived lack of contrast or saturation in post.
Vignetting is a problem (especially when the corners drop +1EV) because at that point, the corners of the sensor are not getting as much light as the center. Therefore, when you go to fix the vignetting in post, the corners will have more noise in them compared to the center of the image. How much this matters, I'm not really sure. I shoot mostly old full-frame glass that barely vignettes on crop sensors anyway.