Sink mobility in WSN is considered to be a challenge for routing the data, as it creates rapid topological changes in the network. Most of the routing protocols available in the literature are prone to high control overhead and are less efficient. An elastic routing technique utilizing overhearing feature, is an efficient protocol with less control overhead for routing the data, from a single static source to a mobile sink. But, when there are multiple static sources, the delivery of data to the mobile sink pose huge delay and high traffic. Here we propose an efficient routing algorithm utilizing the feature of overhearing to route the packets from all the source nodes to the mobile sink. We use a modified version of iterative-1 Steiner tree algorithm with elastic routing, for finding the shortest path to the mobile destination, with minimum control packet overhead. Calculation of Steiner points is dynamic in nature, so as to adapt to the topological changes. The simulation results show that the proposed approach is better in-terms of data rate, energy efficiency and control overhead. Test-bed results indicate that the proposed approach can be used effectively in WSN, where topological changes are frequent.