I was playing with the courier today in the practice mode and here is what i found.(hope to be the first? probably not :D )
1.Full your invintory( and the stash with something cheap)
2.Try to buy an item that you can afford.
3.leave one item down kai click it quickly.
Now you have one item down and the same item on the courier inventory!
DON'T TRY to do in online play only in Practice mode you can do it :P (laaame)
Have good games and play fair :)