If you use just one disc of denim, I doubt it would keep the powder charge from blowing through the shot pattern, as I won't fit tight enough to form any kind of a gas seal. That's fine if you want to shoot stuff close, but maybe not too good for turkeys. A trip to the patterning board will tell the tale for sure. Is availability of wads the problem? I have read of guys making their own wad punched from a piece of hollow metal tube, with the edges sharpened to punch out pieces of thick cardboard for the purpose.
As for the overshot use of demin, as long as it is tight enough to hold the shot in the barrel, it should work fine. After all, that's the only purpose of the o/s card. :m2c: