Using a GameShark Code from the SM64 hack Super Mario Star World, which pulls back the camera to show more of the surroundings, I have created a widescreen effect that doesn't have rendering glitches like the jabo plugin, and you can use any texture pack with it. The main noticeable differences is that Mario is stretched significantly, and the HUD is at the edge of the screen and is also stretched. Here are some screenshots for some comparison. Enjoy!
Camera Code:
8033C685 0005
8033C849 0002
D033AFA1 0010
8033C849 0000
D033AFA1 0008
8033C848 0030
Left: Camera Hack+ Widescreen
Middle: Widescreen
Right: Camera Hack Only
Camera Code:
8033C685 0005
8033C849 0002
D033AFA1 0010
8033C849 0000
D033AFA1 0008
8033C848 0030
Left: Camera Hack+ Widescreen
Middle: Widescreen
Right: Camera Hack Only