I haven't done this but, with some thought..I would draw a centerline on the inside of the decoy and experiment with front and rear position for balance to determine where you'd drill your hole. Then I might use a washer, welded or glued about an inch from the end of a metal rod or wood dowel for the deke to rest on. A few inches above the bottom of the stake, attach a base that will keep the rod stable in the ground, perhaps in the shape of feet. Paint to blend and give it a test.
Or, like on some decoys, put a cone-shaped piece into the hole you drilled that'll rest on the stake.
Just a couple thoughts.