Are you talking about actually removing the content and the option from the menu?
You are a sucker for punishment. Grab DVDReMake Pro. You can pretty much do anything you want to a DVD with it.
http://www.dimadsoft.com/dvdremake/index.php
Btw, you can make anamorphic Xvids if you have a Matroska wrapper instead of avi.
I never saw the point unless you didn't want to resize an anamorphic source.
Edit: Oh yeah, you can do it with an avi, but you have to specify the option in your codec to force 16x9 playback. .mkv automatically plays in widescreen if it's been flagged as such.