I've tried "memory" foam in a custom seat and it worked well; the wife has the optional MG Comfort Gel seat for her V7 and likes it better than the custom upgraded foam change to her stock seat. I am currently using an Alaska Leather sheep skin on my GRiSO's stock seat for hot weather riding, and it works just fine and a lot less expensive than a custom seat upgrade. The sheep skins can be had to fit solo and 2-up seats.
Let us know what you decide...