Hi Peter,
For a while the SA boats were fitted with 40x2mm as Wouter suggests, but I`d advise against it, most of the guys who had them bent or broke them, and have all (except maybe two) gone back to using a dinghy mast section which has a lot more stiffness.
Wouter, if you look at the Mozzie rig, you`ll see that the boom sticks out quite a bit behind the rear beam, so the sheeting angle is not vertical, you put quite a bit of load on the boom when sheeted in hard, under compression. Some of the skinny booms had permanent bends after a while becuase of this, and one or two broke but perhaps due to skippers landing on them in a capsize.
If you changed the rig to a squaretop and shortened the foot length to be just longer than the distance between beams, then it would work, but that`s a whole different discussion ...
Steve