I do not have the same car, but I have had this problem.
I put two piece of hard rubber at the end flange and sort of shock mounted the side pipe.
This allows the pipe to move a little more without shaking the seat and without stressing the flange to the headers.
The other thing I noticed was my first motor mounts were too soft and would allow the engine to rock a lot. I changed to a harder mount. BTW,this took a lot of time as I had to shop around to find harder mounts.
Just my three cents worth.
