Next generation software applications will be required to run on globally distributed heterogeneous assemblies of disparate resources including: emerging computing grids. Such application calls for seamless integration and interoperation between varieties of service standards and architectures developed and deployed using current service middleware standards and architectures. Whilst such middleware adequately provides different APIs, programming models for distributed components and services integration and interoperation at both design and runtime. There is still need for additional middleware services including the support of runtime multi-standard services invocation regardless of the components/service standards and type of middleware used. Based on an ongoing research focusing on self-adaptive software for adaptive middleware, this paper will describe a proposed on-demand (runtime) service invocation mechanism, and the associated service interoperation mechanism.