It would be nice if you could choose between a couple of different warm up protocols in the starting area before a race. it would be like a workout in erg mode, but you would remain on the trainer in the warm up area. You could choose between different pro teams warm up sessions, for example this from team sky (see picture)
Do a warm-up, then enter the race module. You can make a custom work-out for warm-ups. Join in with 4 minutes to go and then race.
I have been searching for the same thing so used this post to make my own custom Team Sky Workout. Just download this file and drop it into your workouts folder within Zwift folder in Documents.
https://1drv.ms/u/s!ArHhEr1nPIdWjG7ZHtI-1VTEgC3C