All mechanical parts fail. A check valve could be installed near the end of the nozzle to reduce the amount of leakage, but it would leak itself after a short time and would also reduce the rate of fuel flow for a given pump pressure. This would waste more energy than the few lost drops could produce.

It may be feasible to relocate all of the inside workings of the pump handle nearer to the end of the fuel nozzle.

I agree that every drop counts to some degree. Not only is the loss a monetary one but also an environmental one too. What if the end of the pump nozzle was encased in a vacuum hose. This vacuum would automatically come on for two seconds after the handle was released. This would suck up any fuel present at the end of the exchange between pump and vehicle. Of course you would run into the issue of who the vacuumed gas belong to but perhaps you could elect to donate the gas in the vacuum to some worthy cause.

Gas vapor reclaimation devices are already installed on pumps in some areas. Like Las Vegas. (Probably Califonia, but I haven't been there in a few years. . .)

If possible the excess fuel could be reapplied to the storage tank.

Better, instead of a vacuum, would be a pulse of air to blow that few drops of gas into the customers tank. The infrastructure for that would be much simpler and regulation friendlier than some mechanism that sucks exess fuel into a system.

Or you could just shake the pump when it's halfway out so that the extra drops fall into your gas tank like I do...