three major factors would contribute to the success of such a test: strong potentiality, unrealized phenomenal nascence, and temporal and physical constrainment.
Simply based on the popular interest in fringe-science and folk-conciousness, the likely “virtual entity” candidate for such an experiment would seem to be a ghost, urban legend, or other widely recognized supernatural entity. The more widely recognized the entity the greater the potentiality. Such phantasms are popularly accepted as straddling the fence between forms of existence and non-existence anyway and would make ideal test subjects on the basis of “unrealized phenomenal nascence”.
In the area of temporal and physical constrainment it would be useful if the phantasm was traditionally associated with a particular geographic area to help limit uncertainties regarding spacial location which might occur upon nascence.
As an additional factor: it might be prefferable, if only for the purposes of provability, to choose some entity with qualities which are improbable through conventional scientific understanding, unsubstantiated by established historical prescident, yet undeniable as an entity in the phenomenal world. For example: bringing Abraham Lincolon or John Wilkes Booth into existence would be easy for skeptics to construe as a hoax (anyone can dress up in period costume and human cloning isn’t too far beyond the realm of what seems possible at this point). But if you could manage a gorgon or Paul Bunyan, who could doubt?