A generalization of the additive Gaussian two-way channel to M users is considered. Such channels contain implicit feedback in the sense that the channel output signals observed by the different encoders are correlated. While the benefits of feedback are shown to be negligible at high SNR, for moderate SNR, feedback can play a significant role in boosting the sum-rate performance. To highlight this potential gain, the special case of the M-user multiway channel with a common output is considered. By taking insights from Kramer's Fourier MEC, a feedback strategy is introduced and shown to strictly dominate the performance of a pre-log optimal non-feedback strategy. Furthermore, an upper bound is derived to show this feedback strategy achieves the sum-rate capacity beyond a certain SNR threshold. Under per-symbol power constraints, this upper bound can be tightened to show the feedback strategy is sum-rate optimal for all SNR values.