The paper introduces a theoretically-grounded conceptual framework for the design of collaborative systems which support expert-mediated interactive value creation involving end-users as active participants in the creation of products and services in principal-agent settings. We show how the problems of information asymmetry and burden of choice in interactive value creation can be addressed by integrating the principal-agent perspective with CSCW models of collaboration between heterogeneous actors. Results of a preliminary application and evaluation through the design of a concrete system for cooperative travel advisory in a real-world setting suggest its usefulness and illustrate how it can inform design practice.