Modern system-on-chips are evolving towards complex and heterogeneous platforms with general-purpose processors coupled with massively parallel manycore accelerator fabrics (e.g. embedded GPUs). Platform developers are looking for efficient full-system simulators capable of simulating complex applications, middleware and operating systems on these heterogeneous targets. Unfortunately current virtual platforms are not able to tackle the complexity and heterogeneity of state-of-the-art SoCs. Software emulators, such as the open-source QEMU project, cope quite well in terms of simulation speed and functional accuracy with homogeneous coarse-grained multi-cores. The main contribution of this paper is the introduction of a novel virtual prototyping technique which exploits the heterogeneous accelerators available in commodity PCs to tackle the heterogeneity challenge in full-SoC system simulation. In a nutshell, our approach makes it possible to partition simulation between the host CPU and GPU. More specifically, QEMU runs on the host CPU and the simulation of manycore accelerators is offloaded, through semi-hosting, to the host GPU. Our experimental results confirm the exibility and efficiency of our enhanced QEMU environment.