I have a bounty for whoever writes a standalone drop-in script that checks if the user browser has a window.nostr in it and, if not, then creates one that instead of talking to a NIP-07 extension, causes a window popup to appear and implements this flow.

This is for web clients that already implement NIP-07 support to be able to easily support this flow without having to change their code (and they don't care very much about customizing the popup).