Seat cover listing wire

[Dino]

On a 69, when installing new seat foam and covers, I know I'm supposed to cut through the middle of the foam so I can attach the cover to the listing wire on the frame. I prefer the look of a flat seat though. I don't want the center to dip down. Should I extend the pocket on the covers so they don't have as much tension on it? Or could I skip attaching them alltogether? 68 covers don't use the center listing wire so how do they stay in place?