I'd assume that securing advanced copies of games can come in the following ways:
1) Being a games journo
2) Knowing a games journo or someone in the industry who can, er, "procure" copies for you, although I'm sure there will be some NDA issues as a result;
3) Working in a retail store and getting to them first (again, NDA);
4) Being approached by a marketing group or team for a game release (as per below).
There's not much of a secret to it, per se - like so many other stories, this opportunity just happened to fall in my lap. A marketing rep happened to stumble across my blog somehow, and he contacted me asking if I would like to do a write-up on the title that he was promoting.
I guess the advice I can offer to others is pretty straightforward: if you haven't already got some kind online exposure, do so now, and make sure people know it exists. There are several ways to do this - sharing blogroll links, adding it to blog catalogues, linking your blog in forum sigs, putting it in your IM name etc.
On top of all that if you update your blog fairly regularly and add the odd review or thought-provoking opinion piece, then someone's bound to take notice...as long as you keep up to date with what's happening and who's who in the industry, it'll at least serve as proof to your future employer that you're passionate about a career in this field.
Personally, I do purchase games that I'm especially keen on and subsequently review them, so that may be an issue for those that are strapped for cash (I see it as an investment in my future, my mum is yet to agree). The prices of games are indeed somewhat prohibitive...
Just my 2c.
Anyway, best of luck with your applications and definitely let us all know how you go! Personally, I'd be interested in how you applied for said positions and how the rest of the process goes...