Okay.
The stylesheets responsible for generating the in-text citations and the
bibliography, are located in the
<winword.exe>\Bibliography\Style
directory. On a 32-bit system, with the default installation, that is:
C:\Program Files\Microsoft Office\Office12\Bibliography\Style
Before you start working on one of those stylesheets, you best take a copy
of the one you want to edit. To ensure it shows up with a different name in
Word, see
http://bibword.codeplex.com/wikipage?title=FAQ#Q8
Now how the stylesheets work? In case of a citation, the stylesheet receives
<b:Citation>
<!-- some i18n information -->
<!-- some extra information provided through field flags -->
<b:Source>
<!-- the actual material -->
</b:Source>
</b:Citation>
What you want to do is abuse the extra information provided through field
flags. For example, you could use the \v flag. When you receive a b:Citation
containing extra volume information, you then will know that the citation
should actually be formatted as a bibliography entry.
Now, in case of bibliographies, the stylesheet receives
<b:Bibliography>
<!-- some i18n information -->
<!-- some extra information provided through field flags -->
<b:Source>
<!-- the actual material -->
</b:Source>
<b:Source>
<!-- the actual material -->
</b:Source>
<b:Source>
<!-- the actual material -->
</b:Source>
</b:Bibliography>
So basically the same as in a citation but with multiple sources and wrapped
in a b:Bibliography element instead of a b:Citation one.
So what you would do is whenever you get a b:Citation element, check for the
v flag, and if it is available, transform the b:Citation into a
b:Bibliography and let the stylesheet process that one. That way, the
stylesheet will output bibliography information instead of citation
information.
An example style where I once worked with this type of flag abuse can be
found at
http://bibword.codeplex.com/releases/view/20331 . Note that it
works completely differently from the Word styles.