We propose a hybrid model to alleviate the notorious problem of premature battery depletion in sensor networks: in a first stage, simple sensors are deployed over an area of interest using any traditional method, in a second phase, more powerful relays are put in positions that allow them to off-load as much of the forwarding burden imposed on the simple sensors as possible. We introduce this model in detail, give a few theoretical results with respect to the optimal placement of the powerful sensors, propose various heuristic approaches for their placement, and present comparative simulation results for these heuristics.