It looks like they use the adapter ring to fit 67mm filters to avoid vignetting with the wide angle lense. Since the number 67 appears in the code for the adapter and the number 60 appears in the code for the lense hood, I'm "guessing" the lense has 60mm threads, which don't exist in any normal filter size.
the guys over that the forum linked me to canon's Asian's site where i was able to downloaded an english version of canon's manual that says the adapter (canon #FA-DC67A) is definitely required to attached 67mm filters.
here's that link: http://support-asia.canon-asia.com/contents/ASIA/EN/0300419501.html (then see page 41)
so, unless you're willing to buy the adapter, there is no apparent way to mount a UV filter, regardless of size.
if this all holds true, then the only thing that makes it strange is why canon just didn't go with a standard filter thread, like 58 or 62mm, then an adapter wouldn't be required. (two millimeters in either direction from their 60 is not consequential). i guess the only answer to that would be your vignetting with the wide angle lens which requires the large 67mm and thus pretty much necessitates the use of a step-up.
which in turn raises yet another question for me:
you said: "...the number 60 appears in the code for the lens hood" but doesn't the hood bayonet onto the outside of the lens and not screw into the filter threads?
the photo i linked above seems to show that: http://www.photographyblog.com/images/uploads_news/canon_powershot_sx30is_hands_on_06.jpg
There has been a LOT of discussion about the auxiliary filter (or extender lens) adapter for the SX30IS over on the DPReview Canon Forum. Guy named Bradly has one and has installed the tele extender lens (Olympus TCON-17) that I have been using with my Panasonic FZ50. Here's a link to get you going to pull out all the required info. (Choose "Threaded View" at the top of the page to locate posts made by Bradly) http://forums.dpreview.com/forums/read.asp?forum=1010&message=36539134