Sylvain is likely correct. Them more URL’s point to a site the higher the ranking. The best method would be to add them to the list but omit any kind of usable URL pointing to the actual site. If Google/Bing/Yahoo/etc can not index it, but you still convey your message then that would be the best tactic.
Perhaps an image of the main URL tied to a javascript launch button to take them there. Since a javascript action that dynamically composes a URL link can’t be indexed it would not promote/pagerank the site the way they want it to. Justice is done with no unwanted side affects.
