[OS X TeX] Can a TeXShop engine give the PDF name?

[Duncan Murdoch]

I'm writing a TeXShop engine for Sweave.  On a complicated project, it 
might be that the current file is Chapter.Rnw, but the engine will 
eventually run pdflatex on Book.tex, producing Book.pdf.  My engine can 
determine all of these names from the Chapter.Rnw file.

Is there a way for the engine to tell TeXShop that the PDF from the 
current typesetting operation is Book.pdf?

I have found that using Applescript to open Book.pdf is not quite 
right:  if the preview was already open from typesetting Book.tex, then 
I get a second copy.  (I don't get two copies from "open"ing it twice; 
there's something different about the way TeXShop opens it as a preview 
than opening it just as a file on its own.)

Thanks for any help.

P.S.  I posted a very similar question on tex.stackexchange.com 
yesterday but got no responses; I hope it's not rude to post here as well.