A real engineer would use miniature divining rods made from bent resistor leads. Be sure to post some action shots for the rest of us.
Or, as franklin said, poke holes through the package if it doesn't already have them. Many already have test holes just for this purpose. Good, sharp needle-like leads are a great thing and would leave nearly imperceptible holes.
If the packaging is clear enough, examination of the seals under magnification and possibly UV can at least identify some bad ones, but not variations in charge state.
X-rays might reveal differences in charged and discharged cells, and would be very practical and cheap if you happen to be a rent-a-cop for the TSA and get a little bored between cupcake confiscations.