Read Les' Cambelt replacement tech write up. He suggests using a metal plate with two holes drilled in it, two long m8 bolts and a socket. I used this method and it worked perfectly, with the engine disconnected! see here
EDIT:
OOps, sorry I thought you were trying to get the pulley off, not the bolt itself. Using a breaker bar, put pressure on it till it bends, then get someone else to tap the bar closer to the socket, worked for me...