High-\(\kappa\) dielectrics are important materials for dynamic memory devices, CMOS gate dielectrics, and energy storage in high energy density capacitors. Adding polarizable inclusions to these materials can enhance and increase tunability of their static dielectric constant by the adjustment of the composition, size, and loading of inclusions. Continuum methods such as dielectric mixing formulas and finite element analysis offer some predictive power for matrix-inclusion composites, but cannot be directly applied to composites with small inclusions, for which quantum and interfacial effects dominate. Here, we develop an adjustable finite element approach to calculate the permittivities of composites consisting of a metal-oxide matrix with nanometer-scale silver inclusions. The approach involves defining an appropriate continuum inclusion and interfacial layer based on the electronic structure of the material and solving the Laplace equation with appropriate boundary conditions. We demonstrate that the model can capture many of the relevant polarization effects in a metal/metal oxide nanocomposite, including those that contain arbitrarily-small inclusions, at a fraction of the computational cost of performing the full quantum mechanics.