How do you power your Core?
The usual way to go is to use a Core GPIO pin to switch a transistor (bipolar or FET) which then switches the supply power.
This way the maximum power you can use is not dependent on the Core but on your power supply.
Even if you used a step-up converter to increase the voltage of one of the GPIOs, you would not be happy, since stepping up the voltage comes inevitably with loosing current, which is not to fat on a GPIO anyway (the power as product of voltage * current will not be increased by stepping up the voltage).