this is a way to get a command block with a command already with a command in it.
this could be a way to get a block placer in vanilla minecraft. just set the command as in the [box] to :/setblock ~0 ~0 ~0 minecraft:{the block of your choice} and put it in a dispenser. recently they gave dispensers the ability to place command blocks. so now they can place than run the command! (I tested and it didn't work maybe try in different versions)