Sam is correct - you could bend the rules to give the warforged a feral template, but it wouldn't make any sense unless perhaps it's something warped by the Mourning.
Do not let your players take feral as a character option. In my opinion, it's far too powerful for its level adjustment and the fast healing ability ruins the idea of hit point management as a resource. You end up creating this character who's nothing but a wild animal that you have to roll dice for.