I have a build with this already http://www.mediafire.com/file/ot30dj54t5wu0jw/mgba.zip
Other changes include:
Dimming (you need to hex edit it to change amount, or to remove) Default: Wii U DS VC
Restart game with the reset button.
GC L/R triggers work half-pressed.
Enabled the setting to skip bios animation.
Added Drill Dozer(Europe) rumble to the overrides.
Alternate bilinear settings, added to test limits, it's actually pretty useless.
My changes aside, you should really try Enhanced mGBA, it's got what you want and way more.
Oh, awesome! That works as well. Have you considered submitting a pull request for just the VI width change to the main branch? I feel like this is important to have in the main build, as it's a fix for a glaring oversight in the Wii port as opposed to an extraneous feature/enhancement.