Not really experienced on this topic but have done it at least once.
As you probably already know, there are two approaches to routing the housings, exit at the first bend in the bar and exit at the top next to the stem. I have only tried the former as I thought that too many bends would induce cable friction.
Even with that approach and choosing where I put the cable stops on the DT did not eliminate the possibility of rub on the HT. Although the housing could be shorter to avoid rubbing while riding straight, but then the radius would be smaller. I know this isn't the way you planned on routing but every thread should have lots of pictures.
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079_PaTrek_Barcon Cables, on Flickr[/IMG]
One way to avoid rub on the HT, besides using those clear stick on's, is to route the housing across the HT, then cross the cable under the DT. If the cable stops are in the right location, the cable will not rub on the DT paint. I have my RockHopper set up that way because it works better with larger radius housings around the cockpit.