It's dead easy. really
A bowl of water - hot, but not scalding. You need to be able to put a hand in there, and fumble around for a bit.
A small saucepan with water.
Put the pan on th heat. When the water warms up, put the polaroid in. Before it boils, lif the pan off. Allow polariod to soak a bit if the pan is small, otherwise hurry up!
Lift the polaroid (still with emulsion) out of the pan, put it in the bowl with warm water. If the emulsion has come off, lift it out then discard the paper from the pint
Now you can gently ease the emulsion off if it didn't come off in the pan.
Put your new backing in the bowl, and spread the emulsion over it...
It took me a long time the first time I tried his, but the result was successful (the one in the technical gallery was my first attempt)!