Force 480p/16:9

[Doc_P]

Hello, First time poster here. I have a 4.3u (gack!) system, onto which I have loaded the homebrew channel.
I'm using Gecko 1.9.3.1 to boot Japanese imports, which works fine.
The problem I am having is that it even though I have 480p (progressive scan) and 16:9 (widescreen) set to 'On' in the Wii system menu, Gecko always reverts back to 480i and 4:3.
I have also tried Gecko 1.07, and it has the same behaviour (as well as losing Japanese character support)
Is there some setting in config.dat or otherwise that can force these settings on? Setting either of the PAL options results in a green-screen and no boot. Force NTSC doesn't seem to have any effect.
Thanks!