How about a magnetic block? B can pick it up just by touching it. It then sticks to him until he stands on a special block which releases it. (Perhaps an existing block like the red brick could be used for this?) The magnetic block might look like the silver cube. B can then build walls with it! Or block bots etc.
The function of the block you propose seems a bit overly complicated lol. When it comes to magnetic blocks, I simply think they will attract metal objects like draggable, bots, metal blocks, rails, motors, and balls (if they're made of metal) within a certain area.
