In a large bowl, dissolve gelatin in boiling water. Drain pineapple, reserving juice in a measuring cup. Add enough water to the juice to measure 1 cup; stir into gelatin mixture. Stir in pineapple and blueberries. Place bananas in a 13-in. x 9-in. x 2-in. dish. Pour gelatin mixture over bananas. Cover and refrigerate until firm.
In a small mixing bowl, beat cream cheese, sour cream and sugar until smooth. Spread over gelatin. Cover and refrigerate until serving. Sprinkle with walnuts.