There has been growing interest recently in transforming small mobile devices from simple service consumers into service providers. The shift from consumer to provider has been made possible by hardware advances that enable small devices to host services. Combined with features like multihoming, small devices can be augmented with other devices to provide new services that exploit their inherent mobility. Intermediary-based middleware has emerged as a promising means for realising mobile services. Essentially, an intermediary is a host on a fixed network that contains a proxy for a mobile service, with clients consuming the service via the proxy. Our intermediarybased middleware ensures reachability and scalability of mobile services, and offers switching among heterogeneous network connections used to link services to their proxies. In this paper, we present further development, based on proxy migration, that enables optimisation of both device and intermediary-side resources, and which enhances mobile service availability.