What about Sir Garfield Sobers. He was a batsman first and then started to bowl as far as I know?
As Zorax mentioned, Sobers started as a left arm orthodox spinner. Batted down at #9 I think in his first few Tests.
Cameron White is another guy who, well I guess he was always classed as an all-rounder as a junior, but there was definitely more emphasis on his bowling. Now playing him as a bowler would be ridiculous - except if you're Andrew Hilditch and you're picking the Australian team for India in 2008...