Obtain nsIChannel for a downloaded file in an extension

[lci...@gmail.com]

I'm working on a Firefox extension which overlays the "Open with..."
form (chrome://mozapps/content/downloads/unknownContentType.xul) and
adds a custom option for bittorent files.

In the "ondialogaccept" event handler, I can only obtain the URI of
the file which is being downloaded. Is there a way for the
ondialogaccept handler to obtain the nsIChannel object that Firefox
created when downloading the file in the first place?

Regards
Ludek Cigler