from Wikipedia:
"A shill, also called a plant or a stooge, is a person who publicly helps a person or organization without disclosing that they have a close relationship with the person or organization."
I think in the sense of a literary technicality you're a shill. I'll concur that the term (IMO) is framed around a smarmy connotation, of which I don't think you're guilty of.
http://dictionary.reference.com/browse/shill?s=t