Maybe try deleting an AP from the ZD. I don't know how it handles that. It might just send out disassociation frames and then stops transmitting and answering any requests, so clients will want to connect to another BSSID.
Note to self: Sniff some packets for that.
But there is no way any AP can instruct any client on which AP it should connect to. It's up to the client always. An AP could send a dissociation frame, but the client can simply reconnect if it wishes.