This paper introduces a methodology for designing service concepts in the specific paradigm of the Internet of Things (IoT). In the frame of the European project ELLIOT - Experiential Living Lab for Internet Of Things -, the Living Lab ICT Usage Lab aims at co-creating "green" services, i.e. services based on air quality and noise measurement. These services are invented in an open innovation setting, by a set of stakeholders and not a given service provider. In this context, the ideation methodology has two main requirements: to design services deeply rooted in people routines but impacting people lifestyle and to design services potentially embedded in the Internet of Things. The novelty of the methodology lies in the coupling of two ad-hoc methods: 1) GenIoT, a method articulated around a generative technique where "designers" are asked to place probes (fake sensors and/or actuators) in their daily environment, i.e. the target service area, and to report on it to the group, and 2) AloHa!, a bodystorming method enabling "designers" to play not only characters but also intelligent objects in order to co-create service scenarios. After a description of these complementary methods, we provide the first results on the application of this methodology.