I just had a great idea: Christopher Mintz-Plasse. Sure, he may not be Scottish, but he's American, and could probably pull off an accent fairly well (after all, his gay-American accent is flawless). He can also swordfight, as seen in Role Models and Kick Ass. And it doesn't hurt that he and Clancy Brown look quite similar.
EDIT: Whoa! We must have been struck by inspiration at the same time, Skinr!