I did it with some of mine. I just drilled a 1.5" hole through the cats as a quick fix when I was 'inbetween cans'. Ran fine on map 2 and was slightly louder. Actualy did a track day like that and the bike ran perfectly.
Cats a fuggin rock hard mate so expect some swearing and to get through a few drill bits. I used hole saws. 3 of em :eek