FEAST is a hardware-oriented MPI-based Finite Element solver toolkit. With the extension FEASTGPU the authors have previously demonstrated that significant speed-ups in the solution of the scalar Poisson problem can be achieved by the addition of GPUs as scientific co-processors to a commodity based cluster. In this paper the authors put the more general claim to the test: Applications based on FEAST, that ran only on CPUs so far, can be successfully accelerated on a co-processor enhanced cluster without any code modifications. The chosen solid mechanics code has higher accuracy requirements and a more diverse CPU/co-processor interaction than the Poisson example, and is thus better suited to assess the practicability of the acceleration approach. The paper presents accuracy experiments, a scalability test and acceleration results for different elastic objects under load. In particular, it demonstrates in detail that the single precision execution of the co-processor does not affect the final accuracy. The paper establishes how the local acceleration gains of factors 5.5 to 9.0 translate into 1.6- to 2.6-fold total speed-up. Subsequent analysis reveals which measures will increase these factors further. (Dominik Göddeke, Hilmar Wobker, Robert Strzodka, Jamaludin Mohd-Yusof, Patrick McCormick, Stefan Turek. Co-Processor Acceleration of an Unmodified Parallel Solid Mechanics Code with FEASTGPU. International Journal of Computational Science and Engineering (to appear).)