From what I know (being raised in a air force family), the Air Force will occasionally take pilots out of their role in order to be a FAC in certain situations. I know a guy who flew f16s but was also FAC certified and I also know a guy who fly f16s but was pulled to be a FAC during the Gulf War. Obviously that was a long time ago, and I have no clue how its done now. Also, both of those guys were initially trained as pilots but then were FAC certified.
* My knowledge is extremely limited, but I've heard a little bit about the topic so I'd thought I'd comment.