They have a new one month free gaming promotion since March already  and i discovered this by accident browsing some forums. So far i did read, every premium subscriber can invite new players. I got my one month invite some days ago already, asking in the forums.

 www.battlegroundeurope.com/index.php/component/content/article/25-promotions-a-offers/1725-recruitment-drive-get-your-face-in-game