A method I have used on occasion is to install a simple ‘air return grill’ over a corresponding cut-out in the drywall.

With the grill not yet mounted, install an electrical outlet inside the wall cavity. Box the cavity as necessary above and below so the new electrical box area is separated from the rest of the wall cavity, save for a small wire hole leading towards the WiFi equipment.

Now the power pack can be plugged into the soon-to-be-hidden electrical outlet. Install the air grill with lovers facing downwards. The electrical area is ventilated and accessible for service, but to casual eyes it is just a simple wall vent.