Many marathon canoe racers I know will cut two criticallly placed tail bone holes about 3-4 in diameter in their seat pad for pressure relief. I have not done it myself, but it seems to be a very popular thing to do if you look at their canoes.
I've never had Chip's issue on my Hemlock SRT tractor seat, but I began having tailbone pain when driving long distances in my car. A cushion with a tailbone cutout solved the problem.