I always thought so too...
That is how Ed van Amsterdam did it....

Everybody always say he won his pro card at a worldchampionship, but that is not true! Ed never won a worldtitle...
He got second at a worldgames show, a competition from another federation, not ifbb!
He had won the dutch Nationals when he was younger, and a European title with IFBB, and combined with his performance at the worldgames he got his procard from Wayne Demillia at the time.... because he was impressed with Ed.
Take the impressed part as you will.....

i just happen to know for a fact that you can apply for pro status after a national Title.
A friend of mine won the Dutch nationals, and was told he could apply for pro status. at the time it was a fee of 200 dollars or something like that.
He laughed his ass off! And said, what the hell would i do on stage with pro's i'll look like a junior competitor.. lol!!