Optimal control problems governed by a class of elliptic variational inequalities of the second kind are investigated. Applications include the optimal control of viscoplastic fluid flow and of simplified friction. Based on a Tikhonov regularization of the dual problem, a family of primal-dual regularized control problems is introduced, and convergence of the regularized solutions towards a solution of the original control problem is verified. For each regularized problem an optimality condition is derived, and an optimality system for the original control problem is obtained as a limit of the regularized ones. Thanks to the structure of the proposed regularization, complementarity relations between the variables involved are derived. Since the regularized optimality systems involve Newton differentiable functions, a semismooth Newton algorithm is proposed and its numerical performance investigated.