A common approach to group multicast in wireless ad hoc and sensor networks is to build an overlay, such as a mesh or a tree, on top of non-member nodes to link the group members. However, the intuitive idea of using multiple unicasts to disseminate the message over the multicast overlay does not take advantage of the broadcast nature of radio transmission. In this paper, we propose to use stateless source routing to perform overlay multicast. By encoding the destinations and forwarders into the packet header, a member node only needs to transmit the packet through the radio once and those neighboring nodes specified in the header will relay the message. Through simulation, we compare our protocol with the Differential Destination Multicast (DDM). The results show that our protocol improves energy efficiency and balances the energy consumption better.