We present a semi-numerical method based on Numerov-Cooley (NC) integration for calculating vibrational corrections to static electric properties of diatomic molecules. The approach exploits the Born-Oppenheimer energy and property functions, utilizing such information in the NC integration of the field-dependent vibrational equation, in a way which exposes separate contributions to the total electric property. The scheme is illustrated by computation of electronic and vibrational contributions to the dipole polarizability and first hyperpolarizability of the KLi dimer. A comparison with results obtained from finite-order perturbation theory reveals various sources of anharmonicity.