In this paper, we present a generic wrapper that enables the optimization of legacy codes assembled in application workflows on grid infrastructures. We first describe advantages of a service-based approach for job management. We then introduce our wrapper, that works at execution time, thus allowing service grouping strategies to optimize the execution. We demonstrate performance results on a real medical imaging application. We finally propose a new ser- vice oriented architecture of the whole system, from appli- cation composition to job submission on the grid.