this is how I would do:
1- Open first document,
2- Parse atrwork tree,
3- Find AIArtHandle(s) you want to copy,
4- Open new document,
5- Copy - duplicate AIArtHandle(s), (AIArtSuite - DuplicateArt)
6- Close first document.
8- Close second document,
9- Job done.
I do not know how to do that without opening the source document in a first place.
It looks like as long as you want the whole contents of the closed file (which I do), placing and flattening is the way to go. I suppose even if you only want pieces, you could flatten and then just parse and delete out the parts you don't want after its flattened.