Combine first 3 ingredients, stirring until coffee dissolves.
Place marshmallows in a 2-quart glass measure. Microwave at HIGH 1 1/2 to 2 minutes or until marshmallows melt. Remove from microwave; stir until smooth. Add coffee mixture to melted marshmallows; stir well. Working quickly, add cereal to marshmallow mixture, stirring lightly to coat. Press mixture into a 13- x 9- x 2-inch pan coated with cooking spray. Let cool completely. Cut into bars.