The advice on this thread has been absolutely unbelievable!

Personally, I favor the Total Quality Management approach -- redesigning the system so the pick can't fall in in the first place. Others have alluded to this. Additional possibilities include using a guitar whose soundhole is smaller than a pick...or moving the soundhole to the side of the instrument...or switching to an instrument without a soundhole (such as a banjo or nose flute).

Or simply using fingerpicks and needlenose pliers.