what about using the record number? Its assigned automatically to each new entry into an endnote library. Although the number depends on a specific database. You can use the corresponding field in the reference and the citation templates.
Your sponsor’s requirements are highly unusual in the publishing field, unless I am misunderstanding them. – Can you provide the detailed instructions, so I can see what they are asking for (if not “endnotes”)? The whole point of citations and reference lists are to minimize the repetition of the information. (I am just another user, and not associated with TR or Endnote.com in anyway).