Save the tops of the peppers—which you have cut off to open the peppers for stuffing—and place them between the stuffed peppers for added stability.
Instead of cooking the peppers in a baking dish or roasting pan, as specified in most recipes, place them in a tube pan. The snug fit makes the pepper sit upright.
Place the peppers in the cups of a muffin tin, which will hold the peppers firmly in place.
Place each pepper in an individual oven-proof ramekin or custard cup. This is also a great system when you want to cook only a couple of peppers instead of a whole batch.
Like these? See more quick tips at Cook's Illustrated.