We propose SAMAC, a Device-to-Device (D2D) communication scheme that can exploit Low Earth Orbit (LEO) satellites as temporarily-available infrastructure with intermediate round-trip-times for supporting D2D medium access of highly mobile ground nodes such as vehicles. We demonstrate how such a scheme can be kept backwards-compatible to, e.g., IEEE 802.11p and we demonstrate analytically and in computer simulations that, compared to unassisted D2D communication or relaying, in situations where a LEO satellite is available it can improve performance in terms of all of throughput, latency bounds, and reliability.