The major difficulty you will face is that the total binding capacity of the PC membrane may not be the same with and without cells. Nevertheless, you should be able to place an upper bound on the influence of adsorption. You will want to fit the data from cell experiments and the data from no-cell experiments simultaneously. This is relatively straightforward with modern software tools. Alternatively, you may want to test other growth surfaces, but my experience is that adsorption is never negligible, and the best approach is to include the support membrane in your PB-PK model.
Analysis is always cheaper than more experiments.
Indeed, this is one of the principal motivations for moving to complex kinetic models. In the case of high lipophilic compound, I cannot often reject the influence of adsorption of drug to the polycarbonate membrane which supports Caco-2 cell monolayer. I would appreciate if any members of PharmPK can advise me on what experimental conditions sould be applied in order to avoid the drug adsorption.