That's what I'd do. I'd add the Centennial as FWH (I've done this a few times and it's been good) and then skip the 20.
Anyone else wondering how sweet this beer will be with all Vienna and 10% Crystal? I have no experience to question this, just a feeling. I've done all Munich before and it's been good but would all Vienna be sweeter? If that's what you're after, go for it.