Barrel assembly is secured to the Steering Column with two 'Tamper-Proof' Screws, which means you have to drill the heads off to remove it.
Once you have it off, it's extremely difficult (or impossible?) to dismantle without destroying the whole thing (ask me how I know!).
On my original Multi I had the same problem.
I ended up gutting the Barrel, and bonding in the end of an old Alloy Actuator for a 'key' (so it could be started without one).
I also had to stick the 'Chip' from the broken key to the receiver ring, so it was permanently 'on'.