To support faster and more efficient networks, mobile operators and service providers are bringing 5G millimeter wave (mmWave) networks indoors. However, due to their high directionality, mmWave links are extremely vulnerable to blockage by walls and human mobility. To address these challenges, we exploit advances in artificially-engineered metamaterials, introducing a wall-mounted smart metasurface, called mmWall, that enables a fast mmWave beam relay through the wall and redirects the beam power to another direction when a human body blocks a line-of-sight path. Moreover, our mmWall supports multiple users and fast beam alignment by generating multi-armed beams. We sketch the design of a real-time system by considering (1) how to design a programmable, metamaterials-based surface that refracts the incoming signal to one or more arbitrary directions, and (2) how to split an incoming mmWave beam into multiple outgoing beams and arbitrarily control the beam energy between these beams. Preliminary results show the mmWall metasurface steers the outgoing beam in a full 360-degrees, with an 89.8% single-beam efficiency and 74.5% double-beam efficiency.