Visa itinerary requirements.

I am flying in to Shanghai and wish to take the train to Erlian (Mongolia) except that tickets cannot be purchased more than 20 days in advance and I will not be leaving China until the 7th of January 2015. I do not want to purchase flight tickets nor trans Siberian train tickets since these are too expensive. Therefore, how do I show my intentions to purchase the Beijing to Erlian train on an itinerary?