I was thinking about your question a little more and wondered if you meant "companion" planting? If so, then the same answer applies as I originally gave. But some plants which don't fall into a rotation plan can be planted as companion plants. The most well known example is planting marigolds (not a vegetable and not in a normal rotation plan) next to tomatoes and other vegetables which suffer from white fly. Many gardeners are sure that marigolds repel white fly, me included. Marigolds can be planted anywhere you like and in the same position each year if you want.