Flaked barley, maltose, Carapils (ie-Carafoam or "Dextrine"), naked oats (malted oat), and I think flaked rye to a small extent can all contribute to an increase in body and mouthfeel. I'm sure there are a few other things.
I just had one of these the other night on draft here in Sacramento. I was surprised to see that the the Port website lists this as a 1.072 OG. It didn't taste like a 1.007 FG (to produce 8.5% ABV). Coffee/cacao extract additions in secondary? Sugar additions in a secondary? Thoughts?