[Exim] SMTP-shovel program?

The answer to Q0521 on the exim-FAQ includes this snippet:

> waiting mail on the MTA's queue. Instead, they get it delivered
> into per-host directories, one message per file, in one of the
> special formats (BSMTP, maildir, or mailstore) and when an ETRN
> arrives, it kicks off some completely different program that
> establishes an SMTP connection to the host and shovels the waiting
> mail down it. That seems to me to be a much neater way of doing

Does anyone know of 'some completely different program', that would
make an SMTP connection to a specified host and 'shovel waiting mail
[sic]' from one of these formats down it? Preferrably a small
standalone utility, as opposed to a piece of some large package..

I'm currently providing ETRN service to one client, not too much
traffic, and its not really a problem, but this sounds like a much more
elegant way.