There is no need to stretch them. You can create a block of infinite dimensions (theoretically anyway, you will eventually break torque) by creating a new block.
As for stretching them, bricks are not models anymore. You can't scale or transform them, they are stuck at the dimensions. This is because the game interprets the brick information, and creates the model itself. If you suddenly decide to stretch it, the game would have to make a new model.
