Fully working as of 09-19-2014 , +updated.

Step 1 :
have a chest ...

Step 2 :
fill your characters inventory ,
with what you looking to dupe ...

Step 3 :
quit and save the game ,
then close the game application and dashboard ...

Step 4:
copy all 3 files from your local hdd to a usb or the cloud ...

Step 5:
now boot back into game ,
and empty it all out into the chest - then repeat Step 3 ...

Step 6:
now go back into the usb and or cloud ...
and only re-copy the save data ,
the one WITHOUT the word world mentioned in it ,
it should be in the middle if you only had the 3 files ...

Step 7 : repeat as needed !

you are basically only reloading the player and not the world ,
thus it WILL let you dupe anything !

sorry for the crude video & information ,
but with any luck you can understand what is going on ...

Happy Mining !