Thanks for the link. I did play around with that code for quite a while,
and while I'm convinced there's a way to get it to work, I'm still
struggling with it. I believe the attached .vbs file does about what we
need to do, but I think I'm attaching it at the wrong location in the
.msi file because things seem to die at the "Session.Database.OpenView"
line with an error saying the object doesn't have that method (or no
error message but still at that line, depending on how I've attached the
action.)

Anyway, I'll probably keep playing around with this, but some food for
thought on why we may not want to implement this as a .vbs:
  http://blogs.msdn.com/robmen/archive/2004/05/20/136530.aspx
In particular, some anti-virus products will silently keep them from
working. That said, I probably need to figure out how to write the .vbs
code in order to (eventually) write the C or whatever else code.