A tweet by Battlefield Bad Company 2 lead designer David Goldfarb that's retweeted by the BFBC2 feed says that even if you stand on your head, they are not adding the ability to go prone in the military shooter sequel: "Fyi we will not add prone based on anything. You can stop asking now. :)"
I know next to nothing about this game. I do however know that giving a negative answer to your potential customers is WAY better than giving no answer at all....