I see a lot of randoms using different strategies to get the free perks. Most involve setting up a trample steam and kneeling behind it.. While those generally work, I personally hate standing still and/or having my back to a wall in this mode; so I figured I'd share my strategy.
It's simple really.. I first buy claymores and make the trample steam. Next, I stack claymores until the gremlin rd, then run around my trample steam while using claymores to take 'em out. It's too easy.