Please post back if you can get it to work. I've been trying to do the same thing.
I tried adding the Universal Dock as a "Digital Music Server", then selected "Apple" as the manufacturer and "A1153" as the model number. I then selected "No" when being asked if I had a remote for my device and it gave me a couple of devices to choose from. "Apple Universal Dock" was actually listed, but unfortunately it doesn't seem to work.