Constructing an embedded device with a real-time and a general-purpose operating system has attracted attention as a promising approach to let the device balance real-time responsiveness and rich functionalities. This paper introduces our methodology for constructing such multi-OS platform with minimal engineering cost by assuming asymmetric OS combinations unique to embedded systems. Our methodology consists of two parts. One is a simple hypervisor for multiplexing resources to be shared between operating systems. The other is modifying operating systems to allow them to be aware of each other. We constructed an experimental system executing TOPPERS and Linux simultaneously on a hardware equipped with an SH-4A processor. The modification to each operating system kernel limited to a few dozen lines of code and do not introduce any overhead that would compromise real-time responsiveness or system throughput.