We analyse how to improve participatory modelling aimed at addressing complex socio-ecological problems when it is driven by one of the actors involved. Whether they are stakeholders, modellers, decision-makers or even researchers, such "actor-driven" approaches lead to significant drifts in the process of engagement and have raised many doubts about the contribution of modelling. The sustainability-driven approach presented here is a method based on a qualitative Agenda, with emphasis on the exploration of the problem and a slow growing quality in model development to reduce the biases imposed by solution finding finality. A Design-Formulation-Output-Appraisal iterative protocol, separate from the Agenda for model development, is proposed to sustain the interactions between modellers and other participants, as well as communication among them. This is to answer the need to maintain oscillations between modellers and stakeholders and to offer a quality context able to avoid the drift of the process. The sustainability-driven method also promotes the need for an Architect that is not only a project management or facilitation role, but has to be a driving force for collective engagement in participatory modelling.