Judging by this picture of him here: www.actors-union .is/felagar/JonPall.htm, he could kind of fit the role of Morfin. In a few other pictures he looks like he could pass for young(er) Voldemort, but he looks old for the part, I think. We mostly see Voldemort in HBP when he's in Hogwarts and just shortly thereafter. I don't think someone who's clearly in their thirties should be playing someone aged 16-22. The oldest we see Voldemort is when he's applying for the teaching position at Hogwarts, maybe when he's late twenties, early thirties or so? But since he's already begun his transformation into Snake-Man at that point, surely Ralph Fiennes in makeup would suffice for that scene. Outside of the Pensieve scenes, I can't think of anyone else this actor could be auditioning for. He's definitely too young and skinny for Slughorn, too young for Scrimgeour (unless they ply with him tons upon tons of makeup), and I don't think there are any more significant roles. Wait, I take that back. XD Greyback, perhaps?

I just wanna say this guy better not get it. Ralph Fiennes should be Tom Riddle as an older form... it makes more sense that way.