Back again!   
A recent response came to my posting of your question elsewhere, which tries to justify linking the apple wand with bardic authority and bardic authority with the role of seneschal.   Although exactly not what you were asking for, and also stretching credibility a bit, I'll pass it on.

    "The Filidh and Ollamh of Ireland were members of a King's court and were employed not only as poets, historians but as advisors in the pre-feudal society. When these legends became feudal tales the role of seneschal took over the functions of the filidh and ollamh.
    The early Welsh histories of Cai given him a number of supernatural links, including going to Anglesey to destroy the monstrous Palug's cat. This could suggest that the early stories of the non-feudal Cai could have him in a more complex Welsh Bardic role. It is only in the later chivalric romances that he becomes simplified into King Arthur's seneschal & foster brother."

I asked for any references about the Palug's cat episode and translation of Fili into seneschals and was referred to the Black Book of Camarthen for the former and an internet site for the latter. (http://www.libraryireland.com/Brehon-Laws/Contents.php) This cited The Brehon Laws by Laurence Ginnell, 1894, claiming
    "Both ollamhs and brehons might as well be called bards on the ground that both were obliged to take a degree in poetry. A loose application tends to involve those terms in the confusion from which we have just taken the trouble to extricate them. Ollamh practically meant a doctor, professor, or teacher of any branch of the Filidecht taught in the higher schools. It meant a possessor of knowledge whose profession it was to impart that knowledge. The right to the distinction was acquired by a course of study extending over twelve years' "hard work," followed by a public examination; and the distinction was formally conferred by the king or chief of the district; after which the ollamh ranked next to the king or chief in the order of precedence, acquired a number of valuable privileges, was respected by the community, and highly favoured by the law."

Elsewhere it suggests that in the original Senchus Mor "though now arranged prose-like on the paper, portions of the text are in regular verse; not merely in metre like blank verse, but in rhyme" – suggesting that bardic skills and perhaps bards were involved in the composition.

I appreciate (a)none of this would stand up in an academic dissertation as evidence and (b)it's trying to relate the apple wand to bardic authority which is what you are trying to avoid, but it might give you another avenue to explore yourself and, again, even if of no use to you, it might be of interest to others who read the thread