Is it possible to Whitelist only ofline players ?

On my server I wanted to allow some people who didn't buy the game to play, but because of griefers ( alot of them ) I was wondering is there a way to only whitelist the non-premium players but allow the ones who did pay for the server to just come online and only have to set a password for the server once .
I have 3 people who play on my server who didn't buy the game and there nice people so I don't want to see them go .

 

There is a way with a plugin by regestering there email and password once they log in... I've seen it before but not sure what it is sorry :/

 

I know there is a plugin that isn't released yet that is supposed to use open id to register on minecraft . Something like that would be awesome if it was released .