Wave Energy Converters (WECs) based on oscillating bodies can achieve optimal energy absorption under certain conditions associated with reactive control. These conditions, in general, are not realisable in practice because non-causal and future values of the excitation force need to be known. In this paper, an alternative approach is presented, where the relationship between the optimal velocity and the excitation force is realised through a simple coefficient of proportionality, thus removing the problem of non-causality. From theoretical considerations and numerical simulations over a range of heaving WECs in different sea conditions, it is shown that such suboptimal and causal approximation, while significantly reducing the complexity and improving the robustness of reactive control, allows the achievement of values of energy capture very close to the ideal optimum.