EASY. dont even need any special tools
take the engine case bolts out (4 of them) then remove the sprocket from the clutch bell.
bolt the clutch bell back on
thread a long bolt through the clutch bell - it will press on the crank and force the cases apart, no damage done
only works on clutch bells with an m8 or bigger thread though. if its m6 the bolt will go into the crank itself and wont push it out. but i havent seen an m6 clutch bell on a cag yet. maybe im just lucky :P
ive tapped it out with a rubber mallet a few times when im desperate as well. but i prefer not to do that incase the crank shafts get bent any.
good luck