If you have the luxury, just stop providing 4:3. Of course, I had a client complain because the 16:9 footage I provided had black bars at the top and bottom – she couldn’t understand why the video didn’t fill the whole screen…
At least start preparing your clients for the conversion – I always explain that ‘they’ (the FCC) will require a 16:9 signal in 2009. That way, at least there’s a bigger reason for widescreen footage.
You could always mask your footage in the editing process and see what your clients think – I’ve found people think it adds something visually.
Jon