[Exim] Filter to match two-extension file attachments?

I am aware of the Generic Executable Filter that Nigel has published.

I'm wondering if anyone has written or attempted to write a filter which
only blocks attachments disguised with two extensions, where the second
(hidden) extension is an executable one (eg xxxxx.gif.exe or
xxxxx.doc.pif)

We are an ISP, and cant quite block all executable content outright, but
I can't think of too many cases where a legit attachment would have two
extensions with the second as a windows-executable one..