I think GentProvocateur is on the right track with this.
Not sure if that type of plastic can be easily heated and re-set to match your radius. might help.
Also, It seems like a denser foam / foam-rubber would work alot better for dampening. especially if some small string slots were cut into one side. The meterial would likely have to be rigid enough so that the width of the slots could be re-cut/fine tuned until the sweet spot is found.
Usually, if an idea cant be easily contructed from items i already have layin around, it quickly loses its fun and motivation goes right out the window ...........................hey look, a squirrel!!!