Since you don't specify what commodity you want to load, I assume you will load whatever the car is capable of. Then, is easy: Use "Instant load" or "Instant unload". It can happen anywhere in rour route as it is a command. M.I.N.'s can't load an entire consist in one shot, just the cars that are over the loading/unloading track. However, as you may know, the consist will move forward automatically, loading all the cars or until commodities are exhausted.