A way around this would be to make 2 copies.  They must be copy/pasted so they are in the same place.  'Boolean difference' the bottom half of one and the top half the other with a cube.  Then you can move the remaining halves together.  Since most of an iceberg is below the waterline the lower half can be stretched.  It is also possible to edit the lower half to make the shape different, as long as the editing stays away from the edges.  

Play with this technique and you can find a way to make the overhang that most bergs have above the water.