I don't believe this is possible. A component has one pattern attached. Of course you can always go in and assign a new one - on a per part basis - but DipTrace offers no help in keeping a list of "compatible" footprints for a specific component. I think it would be a nice feature to have.
I think the idea right now is to have a *accurate* components so you BOM matches 100%, multiple footprints per component might not fit too well with this, unless it incorporated some way of changing the part names (usually suffixes) depending on the footprint selected.
I'm really not that experienced in all this, so please correct me if I'm wrong