> Should I...
> Disallow them entirely since the HTML 2.0 spec says they are unused?
> Disallow would have to mean either substitute some other acceptable
> character on a case by case basis or remove entirely.
You could just mark the resulting documents as
text/html; charset=windows-truetype
and register "windows-truetype" as a character set. With the
appropriate code translation/transliteration tables, other browsers
might be able to deal with them, then.