He worked out that while the MicroSim and the SIM look very different the only things that matter are the contacts which are common to both.
“Electronically, the SIM and MicroSIM are the same so we can cut the rest away and not worry (so long as we are careful),” he wrote.
To begin with, line up the three contact on the MicroSIM with the same ones on the SIM card. You can just look for the 2 centre lines and make sure they are in line and that the top of the MicroSIM is straight. Then get your meat cleaver and press down gently to score a straight line.
It is apparently easy, although you do need a responsible adult to help with the scissors.