The only difference that being able to shoot native 16:9 would make is that you'd have better quality because you're using 100% of your CCD area.
How to control whether your image is squished or letterboxed? Easy - just send someone along with each DVD to adjust the viewers' sets! :-)
Seriously, this is like saying, "How do I sell my car and make sure they only use premium gasoline?"
The viewer is in control over how his 4:3 TV displays 16:9 (or the manufacturer - if no options are provided). My brother-in-law has a big, beautiful Hi-def TV but is too cheap to pay for hi-def cable, so he watches stretched football! It's worse than watching on a tiny b&w TV! Even the cheerleaders are all fat!
It's one thing for him to stretch his pennies, but the TV picture? I've tried to persuade him to change his settings so 4:3 will be letterboxed on his widescreen, but he won't touch his menu settings - he fears the manufacturer had some sort of secret reason for wanting him to view chubby cheerleaders.