report the other site as a spam site to Google or the
duplicate content trick? perhaps a covert link bomb, done slowly as to not attract attention... of course, every thing i recommended is black-hat and unethical, except for the linkbomb but then you have the mighty Goog to deal with when it comes to these gems.
if they domain is indeed that strong, it sounds like only a influx of relevant links that wouldn't be discounted or penalized is the best bet - something from an authority, obviously - which kinda points the weaknesses of a SMO campaign. those kinds of links - while there are many - don't seem to "stick" as well...
captain obvious at your service.
