In RFID-enabled supply chains, in order to securely deliver products, a secret sharing scheme has been proposed. An encryption key of tags is split into shares and the key can be recovered with the sufficient number of correct shares. The conventional scheme introduces sufficient number of dummy tags with bogus shares and prevents an attacker who reads all tags during shipping from obtaining tag information. The number of required dummy tags is decided so that the success probability of the attack becomes lower than that in the brute force manner. When the number of shipping products is small, too many dummy tags are required to prevent the attacker from selecting correct shares with a small number of trial. In this paper, we propose a practical scheme which reduces the number of tags by using extra legitimate tags. An encryption key and its share for legitimate tags are assigned to not only the conventional legitimate tags but also extra legitimate tags, and thus, the number of legitimate tags is virtually increased. By doing this, the number of required dummy tags can be reduced. Extra legitimate tags are separately composed from conventional legitimate tags and dummy tags, then they can be distinguished easily. We show the effectiveness of our scheme by computer simulation.