No "Score x2" cheat code exists for LEGO Star Wars II: The Original Trilogy.
UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, B, A, STARTLEFT, RIGHT, LEFT, RIGHT, UP, DOWN, UP, DOWN, B, A, STARTDOWN, DOWN, UP, UP, LEFT, RIGHT, LEFT, RIGHT, B, A, STARTLEFT, LEFT, RIGHT, RIGHT, UP, DOWN, UP, DOWN, B, A, STARTUP, DOWN, UP, DOWN, LEFT, RIGHT, LEFT, RIGHT, B, A, STARTRed Bricks (found in levels) unlock Stud Multipliers in Extras menu:
Note: Codes disable achievements on Xbox/Steam. Red Brick multipliers do not.