[Evolution] How to add options for attachment display?

[Paul Leyland <pcl23 gen cam ac uk>]

This question arose with Evo 2.0.2 under Solaris 9, if that's relevant,
but I believe it applies to all 2.x on all operating systems

When viewing mail in the preview pane, some types of attachment can be
viewed in-line or can be displayed in an appropriate viewer.  All types
of attachment can be saved to a file.   Some types can *only* be saved.

How can new types be registered with the system so that a double-click
will fire up the appropriate viewer?  If it helps to make the problem
concrete: how do I associate /usr/local/bin/acroread with attachments
that have a .pdf suffix?    Needless to say, I'me really looking to
solve the general problem.

Searching sundry subdirectories of /usr/local/{lib,share}/evolution/2.0
hasn't yet turned up anything useful; neither has consulting TFM.


Thanks in advance,
        Paul