As a voucher? I doubt 1 would fit on Bioshock Infinite's 360 disc. It'd be a separate disc if it wasn't either of those (which I don't see them doing). Maybe that'll be their version of the Filler $10? That's actually not a half-bad idea since if you have the first game, buying it used wouldn't really affect you, but there'd be an incentive to buy it new. Hmm.. either that, or they're bundling it with the CE.
Edit: Nevermind, they're just pulling a Dead Space 2, god damnit. The limitations of 360 discs are just getting more and more obvious with shit like this.