Combine the mayonnaise and cream cheese in a mixing vessel, whisking until the texture is airy and light. Incorporate the majority of the bacon bits and green onions, along with the Parmesan, into the cheese blend, while keeping a small portion aside for a decorative topping; mix thoroughly until combined. Place in the cold storage for 1 to 2 hours until it firms up; form the mixture into a sphere and coat the exterior with the leftover bacon and green onion. Place back into the refrigerator to firm up completely for at least 8 hours or for the duration of the night.