Serverless Authentication Next.JS/Amplify/Cognito - customization of sign up/sign in dialog

Im working through this blog post - https://www.xiegerts.com/post/amplify-ui-auth-nextjs/

Everything mostly works pretty great. One thing I would like to be able to do is pre-populate the 'username' value that you are asked to enter in the sign in/sign up pages that are thrown by withAuthenticator. I see a lot of articles referencing how to change the fields that are used or the ui, but there doesnt seem to be a clear way to pre-populate a field value in the screens.

Is this a possibility?

Thank you!