Given a text representation of a MIME message, how can I recreate the message?

Given a text representation of a MIME message, how can I recreate the
message?

I have a GDB core dump that contains the header and body of a MIME
mutlipart/form-data request message. I need to somehow recreate the
message exactly and send it to my server so that I can debug why my code
is crashing.
The message is from a fairly standard form-data page. All of the
Content-Types are text/plain, except for one that is image/jpeg.
The problem is that the binary part of the body has boundaries already, so
I can't just extract the binary portion and generate the header
automatically via built-in Python MIME code.
Again, I need to recreate the initial message exactly how it was. What is
the simplest way to do this?