Set a defaultEmail in the AuthUI component

[dfcan]

I'm using the React AuthUI component and want to set a defaultEmail when a user signs up. The use case I'm looking to support is: I capture unauthenticated users' emails during a Stripe checkout flow, and I want to give them an option to create an account on their confirmation page. When they create the account, I want to pre-populate the AuthUI component with the email they used in Stripe checkout, but this doesn't seem possible with AuthUI. It looks like there is an EmailAuth component that does support this, but it's buried and I'm unable to import it in my project.
Any suggestions for how else I can proceed?