A true fanatic would suck the egg white and yolk out through a pinhole, inject the emulsion into the pinhole with a syringe, roll it around to coat the interior, wait a week for it to dry and then use the pinhole to make the image.

A negative image from the inside of an eggshell could be "de-fished" with appropriate software and printed as a positive, but that probably does not meet the level of fanaticism inherent in the concept of eggshell pinhole photography.