I though it would be a good idea to tap audio out of a hard drive enclosure to power up the raspberry pi. It worked well, power to the PI is set to 5.25v per suggestion from @Arsenijs .
Some pictures of the power supply hack:
Neat headers for plugging a usb pc port there:
Messy desk testing:
This way only one wall wart is needed, still have to decide between getting power for the oled and buttons from an arduino connected the same power supply or to drive it from the rPi.
Update: A better view of the hack: