I saw this on Neogaf. So here's how it goes. If you "buy" the PS3 demo version and then the Vita demo version and heading back to the PS3 version page and add it to cart, it will show up as free on checkout. I tried it but it doesnt seem to work for me. I see a "try free demo" and I did that for both the PS3 and Vita versions, but when I come back to the PS3 version page, it says 'you are not eligible to buy this'. Can anyone of you guys try this and see if it works and BTW its EU PSN only it seems.
http://www.neogaf.com/forum/showthread.php?t=913127
http://www.neogaf.com/forum/showthread.php?t=913127