I experimented using 3/8" Tight-Lock Foam Rubber Tiles similiar to the foam tiles that you would find in a kids playroom or home gym. I put them over my 1/2 inch plywood. I placed them up side down as the bottom has some grip to it and the track stays in place without any ties or screws. I too use fast track and it made a world of a difference in regards to track noise. I found them on sale at home depot in a 4 pack for under $7.
Very interesting idea, but I have one question.
You mentioned the grip of the tiles on the track which must mean that you have your track on the raw tiles.
What color are these tiles, and will they remain your visual base that you see on your layout?