I had a Fireblade I bought as salvage and it had a crack in the engine casing, I got a good repair using an epoxy resin like the ones you get in Halfords. So long as it is a thin crack and there's no chunks of the casing missing. Worth a try anyway.
This is the sort of thing:

http://www.halfords.com/webapp/wcs/s...egoryId_165691

Or..., I've just bought another product from Halfords that you might like to ask about. Here's the link:

http://www.halfords.com/webapp/wcs/s...egoryId_165691

Anyway, food for thought. I think the first one would work better for what you want, I bought the second one more for filling in curbing on alloy wheels, it's more of a putty whereas the first one will be easier to get into the whole crack and seal it properly.
Worth asking them about, it worked for me at the time.