Incorporating non-verbal data streams is essential to understanding the dynamics of interaction within collaborative learning environments in which a variety of verbal and non-verbal modes of communication intersect. However, the complexity of non-verbal data -- especially gathered in the wild from collaborative learning contexts -- demands efficient and effective analysis. Methodological advancements are necessary to handle this complexity, enabling researchers to derive meaningful insights from these data streams. The advancement of Generative Artificial Intelligence (GenAI) has significantly broadened its accessibility, making it available to a diverse array of users and demonstrating its utility in aiding data analytics. However, the application of GenAI in multimodal learning analytics, particularly within the context of feature extraction for studying collaborative learning interactions, remains unexplored. This study aims to explore how multimodal large language models (MLLMs) can be utilized as part of the multimodal learning analytics (MMLA) process, focusing on the extraction of postural behaviour. The study focuses on an illustrative case study involving 52 pre-service teachers engaged in a physics-based collaborative learning task, demonstrating how MLLMs can be used for feature extraction. The integration of GenAI techniques in learning research promises a new horizon in understanding and enhancing collaborative learning interactions.