It sounds as if you took the bearing bracket off with the fan attached.
I can think of no other way to get the fan off w/o 1st removing the 8mm allen head bolt.
I had one of these round off as well as the metal inside is very soft. This happened while I was trying to remove the 8mm from the fan.
SKTOOLS makes what are called pipe plug sockets. The business end is very much like that of an extension, only they come in different sizes. I simply inserted one that fit, then loosened the allen head. The pipe plug socket has 4 corners, so it's going to grip. I'll try to find some photos of them on the SK site and post here. I have never seen these available anywhere else. By that I mean anywhere that the everyday Joe is going to go looking. Snap-On, Mac, etc. might have them.
I tried posting the URL for the specific web page that has a photo of the pipe plug sockets. When you click on the URL below, you'll get to their home page. In the search box in the upper right hand corner, just key in "pipe plug" . Here's the URL to get to the SK siite:
http://www.skhandtool.com/productcatalog.cfm?tok=1