Neutral leg outlet pluggable detector
There are electrical detectors used for determining if a line is hot. These are one wire detectors. They work by using your body as a capacitive coupling to the environment to generate a pseudo ground. Two of these in parallel, one in each terminal of the outlet would accomplish what you are after, so clearly it is possible. This will still require a human to hold the tester to provide the pseudo ground. without the pseudo ground or any other ground source, it would not be possible.