To be honest, I don't like any of the solutions for this problem. I was thinking, maybe a simple server/client pair written in C.
- Main router monitors new clients entering and leaving the network (server mode).
- Dumb AP establishes an unicast (avoid generating extra multicast noise) connection with the main router server (client mode).
- Main router sends all current info to dumb AP.
- Main router keeps updating the dumb AP with new info until the connection is closed.