Service Oriented Computing is a paradigm for accessing, integrating and coordinating loosely coupled software systems in a standardized way and has gained attention in the recent years within the scientific community. It is increasingly being employed by large scientific collaborations to "wrap" applications as web services i.e. to create an additional "web services layer" on top of existing scientific applications. This enables scientists to easily compose, monitor and run complex workflows consisting of scientific applications that are not only developed and managed by a distributed team of application developers but also run on a distributed set of heterogeneous resources. However, one of the biggest challenges for large scientific collaborations lies in keeping all the web services persistent so that they can be accessed from scientific workflows whenever needed. In this paper we discuss the architecture and implementation of a mechanism by which we can create the web services ondemand, in the event that they are unavailable during the execution of a scientific workflow and thus obviate the need to keep them persistent.