So the remedy is to shut it off as soon as it trips. Solution (1) is the drawing & pictures shown to the right, the yellow block is a little board that pivots on a fixed bolt. The little red dot on the yellow board is a headless nail which is secured by the 2x2 arm in the left drawing. A wire is attached to the other end, which presses against the alarm hammer when the trigger is tripped. From the time the alarm goes off, the headless nail is released, and the board flips up to press against the hammer, takes less than a second.
This pivoted board is kind of complicated compared to the hinge arrangement where the 2x2 is attached to the top of the 2x4, but it seemed like a good idea at the time. If I made another one, I'd use a hinge, even though they have more slop.
Click on these thumbnails for enlarged closeups.
Well actually, I'd use a piece of nylon string (solution #2 --->) an ultra light weight string about 6 inches long (nylon fishing leader, or silk thread) tied tight to the hammer, with a detachable hook & paperclip on the other end to disconnect it from the pull string so the clock can be removed. A piece of light bungie cord, (like an elastic hair tie) in the string acts as a spring, (so it still allows the door to close when it pulls taunt, it should have just enough tension to pull the alarm hammer to the side, i.e. not much), maybe a glass bead guide glued to the side of the clock, so the string doesn't chaff or slip off.
I haven't made this version, but it seems pretty simple. It's probably not as quick to shut off the alarm as Solution 1, maybe 3 or 4 seconds, so if the cause of all this effort really IS a fatigued alarm spring, the version 2 clock won't last as long as version 1, (but if that matters, then you're an obsessive-compulsive efficiency geek & you shouldn't be building this thing anyway. Get a life).