Circuit modeling of high-frequency devices described by tabulated multi-port parameters has generated immense interest during the recent years. In most cases, simple equivalent circuit models (S-ECM) are available to the designers, which correlate well with the measured parameters at certain frequencies, however, deviate at others. Traditional efforts to improve equivalent circuit models are device-specific, laborious and ad-hoc in nature. This paper presents an efficient and automated algorithm to identify appropriate elements for adding to the S-ECM at arbitrary locations so as to correct for frequency-dependent errors. These elements are given as rational functions which can be synthesized into frequency-independent elements. In addition, these functions are found without performing expensive nonlinear optimization. The new method enables the designers to retain their existing physical models while providing a means to capture high-frequency effects accurately.