I've been trying to do this in Wii games with gecko codes,I found resolution floating points in brawl and nsmbwii so far, and I can shrink the screen with them but trying to expand it to eliminate underscan with it just results in the screen being cropped at the original boundaries

The above code definitely has issues with Nintendont either crashes when pressing down on the d pad or on screen transitions depending on the version of nintendont. Also Better Wind Waker works fine for Nintendont so it should work just as well on gamecube as well though I probably wouldn't want to...