Since 2003 (first year of the NT), the only MPO Worlds winner with 0 Elite Series (or non-Worlds Major) wins beforehand:
Nate Doss - 2005
Doss would win his first Elite Series event in 2007 (Beaver State) and his first (and only) non-Worlds Major in 2008 (USDGC).
Has there ever been a person who won worlds without winning an elite series first?