Sure, find a place that does vinyl seat repairs, boat upholstery, etc. they should be able to replace the material and stuff in more foam where needed. Shouldn't cost too much; I had my boat's leaning post done reasonably. I've never seen a Kioti seat do that, maybe others who might have can chime in?
Oh, and I thought of putting some sheepskin seat covers over the existing seats. You could use some low gloss Armor-All on them before doing so, to keep what's left of the OEM seatcovers from completely disintegrating...