The use of "seat packs" to load freight in F-28's was extensively used in WA from the 1970's, sometimes in a mix of Pax/freight.
A canvas type bag, strapped to the seat belts, seat loadings observed, mostly northbound ex Perth, so an equivalent pax weight less the pack carried as freight, way to go as freight in the holds as well.
There is a lack of real world thinking with some people??