Spray a 9-inch pie plate with cooking spray.
In a large bowl, stir boiling water into gelatin. Stir for a minute or two, until completely dissolved. Stir in cold water; pour into pie plate.
Refrigerate for about 1 1/2 hours, or until partially thickened. Push gummy worms into gelatin. Refrigerate until firm, about 2 more hours. To unmold, dip pie plate in warm water for about 15 seconds then gently loosen edges with moistened fingers. Place a moistened plate over the pie plate then invert, holding plates together. Garnish with more gummy worms. Serves about 8.