To solve the key management related problems encountered in symmetric as well as asymmetric key based schemes, recently a public key based scheme known as Certificateless Effective Key Management protocol (CL-EKM) has been proposed for dynamic Wireless Sensor Networks (WSNs). In spite of showing numerous advantages over the previously proposed schemes, this protocol shows some critical limitations. One among these is the method of relying on unicast transmission mode to transmit messages from the Base Station (BS) to all cluster heads in the network. This is because when the network grows in size or when the number of messages to be transmitted at a given time is large, this would cause severe negative impact on the overall performance. Hence, in this paper, we consider the optimization problem of the protocol and propose a solution which enhances CL-EKM by avoiding intensive use of encryption and unicast operations that reduces the energy and delay associated with the communications between the BS and the cluster heads. The performance gains are depicted in the presented results.