Blackhole device WiFi traffic from 1 Cisco WAP - Looking for suggestions

Hello -

I'm looking for suggestions and hoping to get some thoughts.

My problem is that we have employees spending far too long in the restroom, we believe on the internet on their phones. Only 4 stalls for 100+ employees has made this a bit of a challenge.

I've been asked to find a way to limit connectivity to the room, in hopes of limiting time people are spending in the stalls. We run a WLC 2504 with 3 access points covering ~12K sq ft (open floorplan). I was thinking about installing an additional access point into the room with the intention of forcing all WiFi connections onto that AP but am wondering how I could then just blackhole that traffic. I'm not looking to impact device connectivity throughout the rest of the space so changing routes/dns/etc. may not be feasible.

Short of building a Faraday cage or a signal jammer, does anyone have any thoughts or suggestions?

Thanks in advance!