The way to do it:
Use the business/organisation installer to get just the Vive Cosmos/Vive Cosmos Elite driver without Viveport.
I used the offline installer here:
https://business.vive.com/dm/downloads/offlineInstaller
You may need to make a business account to get the files but it is entirely free and the only way I can seem to do it.
Result is no Viveport, just the SteamVR Driver and Vive Console app.
All games continue to run fine.