Executable Domain-Specific Languages (DSLs) are used for defining the behaviors of systems. The operational semantics of such DSLs may define how conforming models react to stimuli from their environment. This commonly requires adapting the semantics to define both the possible domain-level stimuli, and their handling during the execution. However, manually adapting the semantics for such cross-cutting concern is a complex and error-prone task. In this paper, we present an approach and a tool addressing this problem by augmenting the operational semantics for handling stimuli, and by automatically generating a complete behavioral language interface from this augmentation. At runtime, this interface can receive stimuli sent to models, and can safely handle them by interrupting the execution flow. This tool has been developed for the GEMOC Studio, a language and modeling workbench for executable DSLs. We demonstrate how it can be used to implement a Pac-Man DSL enabling the creation and execution of Pac-Man games.