We present an infrastructure in which HPC resources from the Amazon Web Services public cloud are combined with specific grid resources at Ibergrid. The integration is done transparently for the GridWay users through a daemon which permanently monitors the pool of available resources and submitted jobs, managing virtual instances for satisfying the demand under budget restrictions. The study has been proved with a specific application from the Xmipp package, which performs image processing from electron microscopy data and requires heavy high-throughput computing offering parallelization capabilities. The application was ported successfully for such a hybrid framework with the help of the MPI-Start package. Some preliminary results from test runs are presented for a controlled sample of thousand input images. Some inconveniences and troublesome aspects of the deployment are also reported.