I bought a Danmedica gel pad for my F650 single last year. It would have been too tall to strap on the top so I took a carving knife to the foam and modified it to fit, was super duper comfy for a 4.5k miles round Morocco and back. The gel sat on the plastic ribs of the bottom of the seat yet there was no vibration or 'princess and the pea' syndrome.
Now have a F650 twin and have just (about an hour ago) got my seat back from Tony Archer, very pleased with the look and shape of it but as yet haven't managed to try it out, I had a gel pad fitted as the last one was so good.