I don't think there is a way to drill out the rivets without taking the exhaust off the car. There are 2 rivets within easy access from below, but the other 2 rivets between the exhaust and the heat-shield are impossible to get at. There is no way of squeezing a drill in there!
I read this DIY about removing the exhaust, it is a 90 minute job. it seems to be the only way.
http://www.m3post.com/forums/showthread.php?t=299777
If anyone else has a way to remove the tips without removing the exhaust, I am definitely interested.