When your older child comes up to the hospital to meet his new sibling for the first time, have the infant waiting in the nursery with all of the other babies. Then when your firstborn arrives, you and your spouse can walk him down to the bevy of babies and ask him to "pick one out." Obviously, you guide him to his actual kin, but it is a rather sweet and thoughtful way of including him in the process. Another tip — you might want to mention that the package is nonrefundable.
Source: Flickr User skippyjon