DOCBOOK-APPS: Greek identifiers in footnotes

I would like to figure out how DocBook can identify two items per entry
(i.e., a defining standard and a symbol version) in an interface table.  I
would ideally use a superscript for one, and a subscript for the other, but
docbook doesn't expose those as they are formatting issues, not structural
issues.

I'll simply resort to using multiple footnotes per interface.  My current
footnotes use automatically assigned roman numerals.  I would like for my
versions to come from Greek letters, if possible.  I believe there are
entities in Docbook that define these, but I'm not sure how to use them in
a FOOTNOTE ID="XXX" way.

Any idea how to specify the Greek entities?

Thank you!
--Bruce Clavey