I was also looking for a video "how too", but once you hold a 1 1/4" hole saw to the inside of the pipe...you'll realize just how simple it is. You have to get an arbor extension from home depot and a hole saw. You're only cutting through thin pieces of sheet metal. First one you can see right at the rear, second one is further in about 4inches if I remember. The trick is be real easy on the second one, as there is catalytic material beyond that one and you don't want to cut that(or at least I didn't).
The first metal plate came out still attached to the hole saw. Removed it with a screwdriver and did the second one. the second one didn't come out attached to the hole saw and it's probably still in there. A buddy of mine did his and had the same result. Sounds much better, but is definately not a loud bike.
Don't overthink it. It's really not a complicated modification. Just do it (like Nike says)