Tracking base revision for files distributed without a repo

[Benjamin Fritz]

I have a set of scripts which I personally maintain in Mercurial.
These scripts are often useful to other people, so I occasionally
email updates to my coworkers (mostly on request).

Now, these coworkers have no interest whatsoever in learning or using
Mercurial. For these particular files, they couldn't care less about
version control, far that matter.

But when they occasionally email me back a modified copy of the script
to fix a bug or expand the types of data it can handle, I'd really
like to know where to start when merging in changes. They always send
back just the modified files, not the directory I sent them, so I
can't just go off the file created when I do an export, or just zip up
a working copy and send it to them.

I think this would be a good use-case for the KeywordExtension, but
the wiki page http://mercurial.selenic.com/wiki/KeywordExtension calls
this a "feature of last resort" without offering any alternatives
which fit my needs.

Are there better solutions than just embedding the revision in the
file using KeywordExtension? Solutions that allow my coworkers to
continue being lazy but allowing me to benefit from knowing which
version they base any changes off, what to tell them I've changed
since the last time I sent them updates, etc.?