Business-to-Business (B2B) e-commerce is emerging as trading parties are attempting to integrate electronically, to automate exchange of their services. To be able to collaborate, enterprise processes must expose compatible public behavior. It is a common need for a company to collaborate a business with many partners. A problem is that, even agreeing on information to be exchanged, the partners usually expose different requirements for protocol and logic of interactions. Therefore, it becomes necessary for companies to redesign process models to accommodate to a new partner. As the result, the company must engage considerable resources for designing and verifying new process specifications, as well as for maintaining them. In this paper, we propose a framework for flexible modeling of enterprise processes, to support a larger scale of B2B integrations. The proposal is based on a set of concepts of flexibility that enable partial process specifications, depicting thus a wider scope of business scenarios that a company is willing to conform in a B2B context. The complete process specification is made after B2B parties agree on a strict public protocol and enforced by runtime transformations. The proposed framework for flexible process modeling is aimed to speed up integration of partner processes as it increases ability for process matching without requiring changes in their design.