you mean the 135i exhaust with black tips like this?
Yes it is doable. You will need to buy a stock 135i exhaust and bring it to an exhaust shop. there are a few ways you can do it, but what i found was easiest is having a shop cut behind the resonator, weld on a flange that will fit the stock 135i axleback, and then bolting on the stock axleback like thats how it was made. I have it done and it sounds great without being too loud at all. a bit milder than the performance exhaust for 128's.