[Exim] autoreply: complete mail (headers+body) in a file?

Hello,

is it possible when using the autoreply transport (from a filter file or
directly from exim) to specify a file both headers and body are read from,
preferrable with expansion of the file contents?
The file options only seems to cover the mail body's contents, but having
both headers and body in one file would make e.g. generating multipart
autoreplies much easier.

Thanks in advance,

Florian