I know at least one who did it is a very knowledgeable person on here. I believe they cut the muffler out, and put a y pipe to split the single entry to two, and used that as the tips, or made custom tips.

I'm still debating, it just seems eaiser to do or redo, and I have done this on my previous turbocharged car (not a crossfire though), and it sounded very nice.