I have a theory, but not the knowledge to implement it...
i think it should be possible in SP, but i have no idea if it's possible to do in MP..

my theory is this..

it should be possible to add new "jobs" to the jobs board, yes?
so is it possible to add new job TYPES to the job board?
i'm talking about ecsort missions where you get hired to defend a "shipment" from attackers ( whether that shipment is a person or cargo shouldn't matter.. ), like at the start of the SP game..

also, since you can get npc's to "follow" you, then it should be possible to have a transport follow you... yes?
so you should also be able to "hire" transports to take cargo from 1 place to another ( not sure about taking cash off you for the goods in the first place.. )

if it's not possible to have it "follow" you, then maybe have set routes that you escort it on, and take cash off you if the mission fails..??