Maybe align the boxes to boxes next to them when pressing CTRL while dropping the box?

Example: when looking around, the box that will be picked up is highlighted. then you pick it up and move around. now you either drop it, or, if you hold CTRL, a see-through box will appear and highlight the area at which you can then drop the box. This see-through box aligns either to a grid or to the boxes that are around that place.
?