There is also a workaround with 3rd party plugin which I posted on Nuendo forum.
The free Blue Cat Gain plugin can be controlled by midi, and can be linked, currently supporting 8 linked groups.
When inserted in the 6th slot of the channel, it will control the level changes pre send. The you can assign a midi fader to the Gain plugin, and you have a VCA. You can build separate mixer with 8 MIDI faders which will be a VCA mixer.
Cool stuff gonna try it out !!! Thanks for sharing ! Have you got a link to the nuendo forum post?