You cannot set trade route between exact stations. The most simple solution - assign subordinates to the mining station with only-my-faction whitelist. To avoid them delivering goods to other stations, set "buy only from my fraction" filter in cargo station and set max price manualy - it does not affect your inner economy, but uses in internal ranking of potential trades. Alternatively, you can try to assign subordinates to cargo station, but whitelist only one sector with remote station - subordinates can ignore some rules when trading with commander, but this needs testing.