I have a friend who is going on a cross-country reality-television style shoot, using a Sony DSR-300, which is a large, ENG-style DVCam. He's a skinny guy with boney shoulders, and thinks that the stock shoulder pad will get really uncomfortable after long 10 hour days.

What do the pros use to make long stints of handheld shooting more comfortable? Are there 3rd party gel-type pads that can be swapped out for the stock pad?

The Sony's have that gel pad that is said to be the most comfortable available. If the pad on the particular 300 he is going to use hasn't been destroyed, its as good as it gets.

Go to a bike shop and buy a gel seat cover.

Next thing might be to sew some lambs wool onto the right shoulder of the jacket/shirt.

Or get one of those over-the-shoulder brackets that suspend the camera on a wire.

Yeah, DSR300 already have that gel-pad. It's ok to work hanheld for some time, but after 10-hour running around...huh. Like Mike said there is some wire brackets and I think those may be a good solution. Your friend can also putt some extra weight (junk food does the trick very quickly) but that pulls other problems...;-)