A key problem in Rechargeable Wireless Sensor Networks (WSNs) is determining the maximum amount of data that can be collected by a sink over a given time period. This maximum is constrained by link capacity and critically, by the available energy at each node. In this paper, we consider a novel approach to increase the maximum flow rate by exploiting recent advances in Wireless Power Transfer (WPT). Specifically, we deploy a finite number of WPT capable rovers next to bottleneck sensor nodes with the aim to increase the max flow rate of a WSN. We formulate a Mixed Integer Linear Programming (MILP) to determine the routing and the set of sensor nodes that are to be 'upgraded' in order to achieve the maximum flow rate. We also outline a novel heuristic, called Path, to place rovers in large scale WSNs. Our results show it is able to attain on average 85.9% of the optimal flow rate.