Abstract In many embedded systems, the computational power of an instruction set processor is combined with hardware accelerators. Building such combined systems implies co-design of the software that runs on the processor and the hardware that accelerates the embedded application. During the co-design process, the application is partitioned into a software part (running on the processor) and a hardware part (running on the accelerator). In order to ease the iterative process of partitioning, we introduce a novel design methodology. In our methodology, the interface between hardware and software is transparent to the software designer, and is based on dynamic method interception. Because the interface is transparent and generated automatically, the initial all-software prototype of the system can more easily be refined and partitioned. We show that method interception is inexpensive, and we demonstrate method interception in a real-life application. Using our methodology, embedded systems can be designed fast, reducing time-to-market, while still achieving a high run-time performance.