There is much less of this kind of programming today than there was even a year ago, I'm not sure it would be necessary. I can do so with my TV, but I understand not all sets will allow you to. Just tune to the SD version.
Edit: Many shows squeezed down look like heck anyway because they are not evenly stretched in the first place, so now you have a pillar boxed distorted picture.
Edit: Many shows squeezed down look like heck anyway because they are not evenly stretched in the first place, so now you have a pillar boxed distorted picture.