Where can I find references that directly relate drag coefficient increases to passenger capacity reductions? In these notes, the authors state that:


  On the Concorde, a one count drag increase (∆CD = .0001) requires two
  passengers, out of the 90 ∼ 100 passenger capacity, be taken off the
  North Atlantic run.


and refer to this article (paywalled). I've seen other statements that an increase of one drag count is equivalent to 5-10 passengers, but do not recall the source. 

Do you know of any other references that list the equivalence between drag count increases with reduced numbers of passengers?
The book "Airplane Design Part I: Preliminary Sizing of Airplanes" by Jan Roskam covers this extensively.

Nothing tabulated, mind you but the text goes into extensive detail of the equations involved for the sizing of a prospective aircraft and the relationships between the aircraft range, drag polars under various flight conditions and payload weights. 

It also gives the equations for calculating the sensitivity of the change of aircraft range with drag polar and payload weight, which is essentially what your passenger is.

EDIT

Relevant section is in chapter 2 from page 74 onwards.Problem 1 on page 85 is practically custom tailored for your needs here.

Bear in mind there is no one size fits all application of a rule of thumb for this question as every aircraft will differ on account of any number of factors.