Basically 16:9 Tvs simply zoom into the image a bit and chop off the letterboxing giving you a full 16:9 frame. 4:3 TVs display the entire frame including the letterbox.
what kind of timeline are you using? If you have 16:9 anamorphic checeked in the properties it should automatically unsqueeze the image and produce a letterboxed 4:3 image.
In any case I would strongly suggest contacting someone in the techncial deptartment of the station and find out what kind of output they prefer. Also be sure to always properly label your tapes before you submit them. if the techs don’t know what your tape is they won’t know how to boradcast it correctly.