With the fusion of intelligent transportation systems and telecommunication technologies, research and development of vehicular communication-based control algorithms is rapidly evolving. These new algorithms are implemented in complex systems, rely on an increasing number of connected devices, and are often used in safety-critical applications. Since the communication is wireless, the probability of packet loss, radio interference, and communication failures rises alongside the number of communicating agents, necessitating detailed testing of algorithms, particularly in corner cases. This paper provides a proof of concept method for realizing a mixed-reality test system for connected vehicles that uses a software-defined radio to generate radio interference in the physical domain. A measurement campaign was conducted with three vehicles equipped with automotive industrial vehicular communication devices. One of the vehicles simulated the communication of virtual traffic in an aggregated (mesoscopic) manner. Results showed that using the software-defined radio can induce packet losses during mixed-reality testing in a controlled and precise manner. Unlike software-based packet drops, this method offers a more realistic and comprehensive approach by introducing physical interference, better reflecting real-world conditions.