After Garbone's 2-year-old post, I hit ebay for a "CONFORMAX™ Motorcycle Seat Gel Pad- Medium TR". It's almost the same as what Jack bought (just an ever-so-slightly different shape) - but we all three installed them on our non-OEM "Lysette" solo seats.
Mine fit without any trimming or seat modification whatsoever, and it took me all of 10 minutes to remove the seat cover, install the pad, and reinstall the cover. It's completely hidden by the original cover; you literally don't notice it's there... until you hop aboard!