The code thing depends on from where you post, I think. On DW the posting interfaces recognize additional site="livejournal.com" or site="insanejournal.com" added to the tag and when you crosspost to say LJ the crossposter formats the DW user tags to point to the original site too. AFAIK on LJ you'd have to do this manually and insert the links and tiny head and so on by hand (though there are scripts that generate this code for you), but giving the site as parameter does not work.