We consider fast fading massive MIMO systems in Frequency Division Duplex (FDD) mode and propose a communication scheme based on Device-to-Device (D2D) cooperation and statistical channel state information (CSI) feedback. User terminals (UT) are conveniently clustered and cooperate within a cluster to create a virtual MIMO at a target UT via D2D communications. We propose and analyse the use of D2D CSI at a massive MIMO base station (BS) to enhance performance compared to statistical precoders oblivious of the underlying relaying links. In the case of uniform linear array (ULA) at the BS and slow fading channels for D2D links, the structure of an optimal precoder is characterized and an algorithm for optimal power allocation is proposed. The average sum rate of the proposed communication scheme is analyzed by numerical simulations and it is compared to a baseline protocol oblivious of the relaying CSI.