I found a comfy, reasonably priced Airhawk type seat cushion for you boney rumped old guys like me. I replaced the guts of the popular Wall Mart cushion with this self-inflatable pad.

I’ve used this pad from the SkYMall catalog on longer flights and never thought of trying it on the bike.

http://www.skymall.com/shopping/detail.htm?pid=204049995&c=

I happened across a cheaper version from REI that looks to be as well made as the SkYMall pad.

http://www.rei.com/product/746401/rei-lite-core-sit-pad