If the shape/size of the SnS potentially lends itself to using a snuffer of some kind, it would be worthwhile to have a simple plate with basic handle of some kind. Not all kettles seal well, even with good vents.
On a standard Weber flip grate, is the SnS coal area larger, smaller or about the same size? Even if the snuffer plate didn't fit 100% of the top area it should still be very effective.