Ye sure thats easy.
You can place a position 3d in your character scene. Then you can create a separate scene for your shape, and it should appear in you resources. So lets just say your parallelogram scene is called, cube.tscn. Then you can do something like:
var 3dshape = preload("res://cube.tscn")
And then using your position 3d you can write
var b = 3dshape.instance()
b.start($position3d.global_transform)
get_parent().add_child(b)
And although this isn't very clear, it should give you an idea of how to do it.