BCC'ing a secret stripe address would be OK, until you accidentally put it in CC instead.
Edit: That said, finding a secure way of achieving this kind of convenience would be pretty great. Really, the only way to rival Google's new attach money to emails in Gmail feature.
If someone were going to attempt this, they would look at far more than just the "From" address. There are a lot of email headers and other data points that can help figure out the identity and authenticity of the sender.
BCC'ing a secret stripe address would be OK, until you accidentally put it in CC instead.
Edit: That said, finding a secure way of achieving this kind of convenience would be pretty great. Really, the only way to rival Google's new attach money to emails in Gmail feature.