Late to the party, but here's a description of what I did. I have the Yamaha comfort seat, which was better than the stock seat, but I've still had some serious issues with my tail bone going numb/sore/painful after an hour or two. I've considered different ways to solve this, but finally went for the DIY approach. It worked wonders, and I can now ride 6-7 hours before I have any kind of discomfort in the tailbone. It took me about an hour, and hardly any expences.
Please note that following the instructions below will be a chance to take, it may not work for you, and you will off course ruin any warranty on the seat. I take no responsibility whatsoever for anything ever under any circumstance. That said, I'm very happy with the results I got.
Here's what I did, the idea is to create a void space under your tailbone:
See photos: https://imgur.com/a/C2GQrl2
1: Remove the staples in the aft part of the seat, and pull away the cover and a layer of plastic to reveal the foam inside. Be careful not to damage the cover or plastic!
2: Remove the screw that you find under the foam. Grind the head of the screw a little more flat, and use epoxy glue or similar to round of the screw. See photo.
3: File or sand away the edge on the rear part of the plastic seat pan. See photo. You want to remove the edge completely in a 10-15 cm wide area.
4: Using a sharp knife, remove the yellow foam in an area that's approximately 5 cm wide and 3-4 cm long. Chamfer the edges, you don't want any vertical transitions, they will feel like an edge.
5: Re-install the screw and glue it to the plastic seat pan.
6: Put the remaining foam, plastic and seat cover back in place. Stretch the cover material into place and staple it back on. Use 6 mm staples. My staple gun was not powerful enough, so the staples went about halfway in. I used a hammer to make them go all the way.
