Certainly sounds like a worthwhile experiment, Dennis. I think I'd try a card or 2 overshot wads on the powder first, then the greased cloth, then overshot wad.
Too - post it notes might work.
Some here have said paper post it notes (or coin wraps) wrapped and glued around shot charges shoot too tight like slugs- no spreading - but - did they pattern at longer ranges, like 35 to 45 or even 60yards?
The shot concentrators sold by many suppliers in England in the 1800's (noted by WWGreener in his book) for use in CYLINDER bores, had 'different' ranges, identified by the colour of the paper wrapping. One of them, green, I think, was for shooting wolves and deer out to 50yards OR ducks at something past 75 or 80 yards. These apparently worked like slugs close in and nice patterns further out. One such 'concentrator' put 28 pellets through a card of paper 4" X 7" at 75 yards - in a shooting contest by an English sportsman using a 14 bore SXS w/26" tubes at St. Louis and an American market hunter with a 12 bore SXS with 4' barrels. The American market hunting Gentleman called the Englishman's shotgun a "little pistol", indeed it was, compared to the 12 bore with 48" tubes.
Perhaps these paper wrapped concentrators could be 'adjusted with slits, etc' to give different ranges with our smoothbores as well.