Back in the 80s I used to use weatherstripping (that you purchase at the hardware store to insulate around doors and windows and such - foam, with adhesive side to it - comes in a roll.) I applied it right on the top of my toms (toward the edge of the head of course) This was before Richie Ring, Studio Rings, Remo-O s were around (or before I knew about them). It worked quite well for the sound that many were going for at that time - muffled more than rings (I used it on my Remo CS Black Dots.) Of course how much you use determines the degree of effect.
Well, I had a BD recently with a real nice Remo White Ambassador on it (had bought and installed before I discovered the current heads with built in rings in them). So, I decided to use this weatherstripping as opposed to the felts (that frankly I just don't like at all). The end result is very controllable and can be used in a way that looks great too.....see the attached photos. Apply on the inside, they sell it in black white and gray - I suggest you match the color of your head. I used white on the inside of this head.
Thought I would share this idea as I have never seen it done before.
John