I've become quite an expert at opening up disposible lighters, although I have not yet tryed bic. I use a saw blade of any kind, whatever is at hand (usually a hegna* or junior hacksaw blade). I saw part of the way through, about 1/3 just below the working bits, and then just use a knife blade to prize the rest off. It doesn't take much effort at all.

* For those of you not familiar with a hegna saw, it is a type of electronic scroll saw mounted on a platform. The blades are very thin and about 3 inchs long and flexible. I carry a shortened one in my wallet.