Support for Bcc: should probably be added to the mint_hashcash.py script. The problem is the ability to add the token to the header, without letting others know that it exists. The only way I can see for this to happen is to send multiple emails.
However, the mint_hashcash.py script is set as the "editor", so it would have to call sendmail, or some other MDA externally. Mutt has builtin support as an MDA, so it would be silly to use an external one. Would be preferred if the Mutt MDA could be called, or the ability to create multiple mails, and send them in one swoop.
Mulling over options and ideas here.