On many store bought keys, you can slip a hack saw blade through the existing slot, and increase the slot's length. I have a selection of metal cutting saw blades that I use for this purpose. You still have to clean up the slot with needle files and abrasive. I pin through the top of the 45 deg. angled flat right next to the vertical. You have to be careful to only go just through the slot and minimally into the wood beneath, as the stock curves away and it's easy to pass the drill bit right through...as me how I know this.