try using satishes 3dle plugin at the top is scale x and y controls undo the little padlock locking these together and use the slider to adjust accordingly on the y scale.
Then use crop top and bottom to adjust for widescreen you may have to guess a little for the correct proportions.... Good luck

"Can anyone recommend a way to get footage shot in 16:9 letterbox into a Widescreen format so it may properly display and fill the screen on a widescreen TV? "

Not sure 100% of your quest... I guess I'll assume you've got a widescreen image sized to fit in a full sized frame (720, 704, 640 etc...), with letterboxing top and bottom.

If you wanted to go to DVD, size the frame to the width you want it - ie. 853, 940 or whatever, maintaining aspect. Now crop the height to 480 (or PAL equiv). Then resize the frame to 720 width with aspect off, so that you get a picture that appears squished width wise. Encode that to mpg2 (DVD spec) checking the 16:9 box in the mainconcept custom dialog to set the flag for DVD players and player software. Optionally you can use something like restream to set the height flag to 540.

[Can do the above as separate steps or combine as possible. Remember that VV4c can/will generate letterbox frames for you.]

If you wanted to go to something like DiVX, WMV, Real etc., just crop off the black bars.

hope something there helps...

If I understand right then 16:9 letterbox IS widescreen. Letterbox being widescreen one and the same unless you have blackbars on 16:9 which will leave a more narrow aspect ratio from my confusion here I thought that you were refering to anamorphic to wide screen but either way or any way satishes plugin 3dle could still be used I dont know whether this would influence picture quality I hazaard a guess and say I dont think it would