The motion of a wave energy converter (WEC) can be described in terms of an integro-differential equation, which involves a convolution operator. This convolution term accounts for the effect of radiation forces acting on the device and represents a computational and representational drawback both for simulation and analysis/design of control/estimation strategies. We present herein a moment-based strategy to compute a parametric form of the radiation force subsystem for multiple degree-of-freedom WECs. The strategy allows for the computation of a model that exactly matches the steady-state behaviour of the target system at a set of user-defined frequencies, while retaining the underlying physical properties of radiation forces. The potential and capabilities of the presented method are illustrated considering a CorPower-like device (heaving point absorber) as an application case.