The scalar-gauge pair formulation promotes gravitational coupling constants to conserved charges, clarifying their role in extended black hole thermodynamics. However, its original incarnation restricts these auxiliary scalar fields to rigid, nondynamical configurations. In this paper, we introduce a local, dynamical completion of this framework. By constructing the kinetic sector from a defect, which is the difference between the top-form field strength and the associated gravitational Lagrangian density, we allow the scalar to propagate as a genuine massive degree of freedom. Crucially, this local sector acts as a charge-preserving massive scalar backreaction, ensuring the thermodynamic coupling remains a conserved integration constant rather than a locally varying field. When evaluated on constant-coupling configurations, the auxiliary stress-energy contributions vanish entirely, perfectly preserving the original black hole solutions, the first law, and the Smarr relation. We illustrate this construction using the cosmological constant and the Gauss-Bonnet coupling.