Force 1 x 4 piece:
Pause game play and press Up(2), Down(2), Left, Right, Left, Right, B, A, Start. The piece currently falling will transform into a 1 x 4 piece. Note: This may only be done once per level.

Level select:
Press Start to pause game play, then press Up, Down, Up, Down, Left, Right, B(2), A.