You need to thin the tip of the hook a bit (from round to angular) so it can get a good "grip" under the cap.
What do you do to fix the finish after you thin it out?
(Incidentally, though I hate to mod something so hard to get, there is the countervailing consideration that a "blade catch" on a knife might be construed as making it a weapon--whereas if the "blade catch" is demonstrably modified to be a beer-bottle opener, I imagine that problem might diminish.)
