Yea, we have something similar.
Make each of objects "Drag & Drop" behaviored, and if you need assign an additional instance variable flag for "locked" status (if you want them to be approximately droppable). Then if locked=1 set sprite x,y to the box x,y. You will have to do a check to see if the mouse cursor is over a "box" sprite (assuming you are using sprites for individual boxes), in order to cause the tool to jump to the box slot.
I am kind of newbish too, so don't take what I say as gospel, lolol. I am a server programmer foisted -- somewhat unwillingly -- into Construct.