This paper considers the problem of designing static-state feedback laws for output regulation of square affine nonlinear systems. The approach taken is to use input-output decoupling techniques to simplify the output regulation task into separate single-input single-output regulation tasks. In the case where the input-output decoupling matrix is full-rank, this approach yields the well-known input-output linearizing feedback law. In the case where the input-output decoupling matrix is rank-degenerate, it is shown that a static-state control law for output regulation can be constructed as long as the system can be input-output decoupled via dynamic feedback. The internal stability of the closed-loop system obtained using this approach is analysed.