Weight the lure blank to sink in a jar half filled with denatured alcohol (or pure alcohol), screw on a lid with a small hole in it------then suck out the air with a food vacuum pump (or whatever you have handy). If there is a hole (due to the higher pressure inside the lure) you will see bubbles exiting the blank joints etc, when you remove the vacuum alcohol will be forced into the blank by the external air pressure--- the alcohol should eventually evaporate out if you put it in the sun.
Once set up this will take no time to do each lure.
Pete