Andy, the key word there was friendly. I've seen some pretty outrageous modifications done to all makes of mopeds, even the Seven, but they were hardly easy to pull off by most peoples standards. It can be done, just not with ease.
if you are going to be hacking and welding up a pipe to work, you might as well just make the pipe bend directly to the right or left of the motor. At that point it might be easier to just make your own pipe from scratch to spec and get the motor to variate (or have a variated rear pulley!) and have yourself a completely ridiculous ripper and rally stopper!