This question sparked a lively discussion and debate on this rather sensitive issue.
One piece of the original question was:
What ceremony / ritual must be performed (if any) to formally designate a woman as a specific man's pilegesh?
What ceremony / ritual must be performed (if any) if/when the couple wants to dissolve the pilegesh relationship?
No one ever provided an answer. I am looking for one of two things:
Evidence that a specific ritual is used to acquire a pilegesh
Evidence that no specific ritual is required to acquire a pilegesh
Also, if the ritual includes a written document, what is written into this document?
(There seemed to be general agreement over here that a pilegesh does not receive a ketubah).