Possible, yes, easy, no. There is no non standard exhaust available for the BIS from what I know, also a big bore back box tends to reduce power unless a lot of other work is done to go with it. There is no point getting any after market exhaust, you would have to modify it so much that you would be better off getting a custom exhaust made. It is a single peice exhaust so very different to almost every other car.
