and yes its possible to stack them up (either as preplaced doodads (the easy way) ) or as buildable units

(the harder way which would require some triggering, but u could build up lego walls and stuff)
actually that gave me an idea... u could use lego blocks to build up castles and stuff using some triggering that figures out what blocks are dependant on other blocks and then blow holes in the walls and stuff... unfortunately i guess u couldn't do multiple floors