Er... ToC takes into account the subpages headings http://en.wikipedia.org/w/index.php?title=Wikipedia:Sandbox&oldid=119738...
That shows transcluded pages, not subpages.
And I thought I was being stupid again...
I think the best you can get is to an automated list of the subpages, not the TOC from them.
Yeah, that's what I expected - well, it didn't hurt to ask...
Thanks!
-- F.