1) Used "other" easy setup wizard to gain access to turn off DHCP on slave router
2) Set slave IP to be out of the DHCP range of the main router, but within the subnet.
3) Setup wifi SSID, password etc to match the main router, but use different wireless channel.
4) Put slave at opposite end of house, connected over powerline.
Bingo... Seamless wireless transition throughout the house and garden. Can also connect devices to the slave via cable.