Yup, it's the clutch fork. All you need to do is put some grease on the pivot point, just inside the bell housing. Bit fiddly, but not difficult.
1. Unbolt and remove the passenger side strut brace (just to give you better access).
2. Undo the two bolts holding the slave cylinder to the bell housing, and just move it out of the way so it's not pushing on the fork (no need to undo the hydraulic line).
3. Gently slide the rubber boot off the top of the clutch fork. You should now be able to reach a finger in behind the fork and feel for the pivot point. You'll have to work by feel, but should be able to reach it.
4. Once you know where the pivot point is, get a dollop of grease on your finger and apply it to the pivot point. I used red rubber grease as its nice and tacky. Work it in as best you can. Wiggle the fork back and forth a bit to help.
5. Once done, replace the rubber boot over the fork and reseat it properly on the bell housing. Reattach the slave cylinder, and then the strut brace and you're done. Work the clutch a few times to work the grease in and confirm the fix.
I did this a few months ago and it got rid of that god awful creaking. Some say you need to repeat the process regularly, but so far the noise hasn't returned.