Forwarding an Email in the Body of a Message

I work with a system that accepts incoming emails for further processing of various kinds. The system expects to receive a forwarded message and all the headers it came in with all in the body of the email, rather than just modifying the envelope To and forwarding to the next server - it uses the header information as part of the processing, so it needs to know where the original headers stop. This means I can’t just forward the message using Cloudflare email routing because the headers are continuous. I can build a new EmailMessage object in a worker, but it doesn’t appear there is a way to actually send the message on even though I have verified the forwarding address. Any suggestions?