Deploying Skype for Business 2016 client - change default username from "username@domain.com"?

I am deploying Microsoft Skype for Business Basic in my organization.

Users are licensed in O365, but their Exchange mailbox will still be on-premises.

I've configured a silent install by extracting they above link using the .exe parameter, and then running the setup.exe /admin to generate a silent install MSP file, but no other configurations.

When I deploy the client, I notice after a user opens it, it defaults to "username@domain.com" in the sign-in address box.
Is there a way to make that a bit more friendly for the end-user so that it defaults to their own e-mail address/UPN? Maybe a registry trick?
I see new values created like "ServerUsername" in a test client after I login, under HKCU\Software\Microsoft\Office\16.0\lync

And, if it can default to their company e-mail, will it auto-sign in, even if the login is going to be their sync'd O365 credential (using dirsync, no sso implemented currently).