I've got something close to that in my past...
Years ago I worked for a managed service provider with about 100 different companies all within one managed network. Part of the consumer contracts were that companies would buy their components, but would not have the power to manage them while under the contract. Also, they could only purchase approved hardware for their infrastructure (all Cisco).
Every once in a while we would get a call that people's interwebs were going super slow, or not working. In most cases they weren't allowed to have wireless, or the company wouldn't purchase new equipment for various reasons... whatever. Anyways some dude would bring in a router he got at best buy and plug it in. Usually I was able to spot it the minute someone called in with problems, email the user (if I could ID them directly), their supervisor, and maybe the CTO of the company that an unapproved device had been installed and blah blah blah. Then shut down their port until they called us to sheepishly appologize.
Better still we would get people calling in for help with their "home" wireless router. This wasn't something we supported but the service desk usually helped out to be nice. I'd overhear conversation queues and start investigating and find out that the customer was doing this from their cube. I'd shut them down and have an evil sysadmin laugh about it.
One time, though, someone got it right. They looked up their local networking and managed to configure their home router to mimic local DHCP. If they were really thinking hard, they would have set the range higher so there wouldn't be an overlap. After overhearing some service desk calls I quickly located our rogue DHCP client, shut it down, and started pushing out MAC filtering to our switches for that company (repeat offenders) for all the well-known consumer network equipment MAC addresses. So any time a D-Link, Linksys, what have you router was detected, the port would shut down for 2 minutes. I watched this happen the day after this incident as the dude walked around his office shutting down ports left and right. His supervisor had been informed that it wasn't allowed, but the dude was relentless.