This is my first post, and I know I should introduce myself first, but need to get piccies done to post up! Anyway, I did this a couple of years ago when I lost the keys to my new bike (D'oh!!) before I even got to ride it.
I just went straight in through the key hole with the biggest drill that would fit (about 10mm I think). I did this with a tank full of petrol, but went very slowly indeed to avoid sparks. It didn't take too long to break through the 'key hole' bit and expose the tumblers which could then be manually clicked out of the way.
It was a bit of a fiddle, but worked for me...