In this paper, we describe an opportunistic model for human-environment interaction. Such model is conceived to adapt the expressivity of a small lexicon of gestures through the use of generic functional gestures lowering the cognitive load on the user and reducing the system complexity. An interactive entity is modeled as a finite-state machine. A functional gesture is defined as the semantic meaning of an event that triggers a state transition and not as the movement to be performed. An interaction scenario has been designed in order to evaluate the features of the proposed model and to investigate how its application can enhance a post-WIMP human-environment interaction.