Choreographies describe the interactions between two or more services from a global perspective and specify allowed service conversations. Choreographies typically do not rely on static binding, i.e. the participating services are not selected at design-time of the choreography. Some services might only be selected at runtime and this selection has to be propagated in the case of multi-lateral conversations. Hence, the notion of service referrals (also called link passing mobility) is recurrent in choreographies. In past work, we have proposed BPEL extensions for describing service choreographies, namely BPEL4Chor. This paper closely investigates the link passing mobility capabilities of BPEL4Chor and illustrates their semantics using Pi-calculus.