The Pharaoh Shot only uses energy when you either press or release the B button, so you can have unlimited Pharaoh Shots doing the following trick.

At the weapon menu highlight the Pharaoh Shot, press and hold the B button, then resume playing the game. You will start charging your shot as if you had already fired it. Run the charged shot into an enemy so that you don't release the B button. This will hurt the enemy but not drain any energy from you weapon meter.