Stir together the stout, soy sauce, Worcestershire, and garlic in a large glass bowl or baking dish. Add the steak and allow to marinate at room temperature for 45 minutes or in the refrigerator for 3 to 6 hours.
Heat the grill to high.
Brush the peppers and onions with olive oil. Grill until the onions are soft and have prominent grill marks, and the skin on the peppers is charred and starting to peel away from the pepper.
Add the peppers to a brown paper bag, rolling to seal in the steam. Set aside while you grill the steak.
Remove the steak from marinade, pat dry, sprinkle liberally with salt.
Grill on both sides until medium rare, about 4 minutes per side. Remove from grill, allow to rest.
Remove the peppers from the bag, peel off the charred skin, cut the soft pepper into strips.
Thinly slice the steak.
Stir together the sour cream and the blue cheese.
Fill the rolls with steak, onions, peppers and cheddar cheese. Return to the grill, close the lid and cook just until the cheese melts (if the bun starts to burn, move the sandwiches to the upper rack of the grill).
Remove from grill, top with sour cream and green onions. Serve immediately.