No-mess method: Combine egg yolks, cheese, mayonnaise, sour cream and green onions in 1-quart plastic food-storage bag. Press out air and seal bag. Press and roll bag with hand until mixture is well blended. Push filling toward bottom corner of bag. Snip off about 1/2-inch of corner. Squeeze yolk mixture from bag into egg whites.
Picnic or tailgate tip: Prepare filling in plastic bag, as above. Carry whites and yolk mixture separately in cooler. Fill eggs on the spot, pressing filling out of snipped corner of bag.