Little late to the party on this one, but found it while searching for something similar and decided to take a shot.
Try this - doing it from memory, so cli syntax may be a little off.
neighbor x.x.x.x advertise-map ADVERTISEDROUTES non-exist-map T...
I had this problem on a couple of my flexconnect APs. What I ended up doing to fix it was create an AP group per location with "dummy" interfaces assigned to that wlan (eg, create interface "Boston", and give it vlan tag 192 with no IP addressing ass...