Something that I have done in the past for folks who don't have a registry is buy them a doorknocker with their new last name engraved on it! It has been a huge hit, especially among those who are already established and don't really need any household items.

You could also consider any kind of specialty painting that has their name on it. Something that I have also given in the past is a rural painting with a mailbox and the couple's name on it.

Of course, you could always just give cash also.... since most couples could use it for honeymoon expenses.

The music idea is a great one, since your boss is musically inclined. Maybe a gift certificate to an online music store? That way they can choose something they like together and that neither already has.

Let us know what you come up with!