The car industry uses sound deadening pads on the inside of panels which are cured when the paint is baked, but I'm not aware of any that would survive inside the primary chain case or rocker cover, and they would not look very pretty on the outside.
How about fitting an aluminium pad on the inside? It would need mounting holes to be drilled in the covers, which certainly wouldn't be seen on the rocker cover. A quick check with plasticine would tell you how much clearance you have. The mounting holes would be yet one more source of potential oil leaks, but we're used to chasing them.