Thanks HT - I'm getting used to the UI now :)
The option has moved though and should be updated in the KB. It's under Settings >> Show Advanced Options >> General
(there should be an image here)
That seems to work. Here are some telnet results:
00:1a:1e:08:59:79# show ip interface brief
Interface IP Address / IP Netmask Admin Protocol
br0 192.168.104.242 / 255.255.0.0 up up
00:1a:1e:08:59:79#