Hi,
Tested this earlier - video shows it in action here: https://www.youtube.com/watch?v=UFtW-vTi7ZI

Steps:
1) Have any number of repair turrets placed
2) Place a yellow logistical storage chest inside the towers supply area
3) Place 1 of the item you want to dupe into your Logistical Trash Slot
4) Ghost place the item down onto the floor within the repair towers build influence area
5) Watch as the tower takes infinite of the item from your trash slot to build the ghosts
6) Use the dismantle tool to remove the item you ghost placed and store them into the Storage Chest, repeat step 4 -> 6.

Notes:
- Using Factorio v1.0, mod version v0.5.5
- The chest in step 2 is not required, but makes it easier to dupe faster.
- By "Entity" I mean any placeable entity that can be placed as a ghost.