Actually, the perf section of the board where you are tapping into, is pretty much one area I have never sourced power from.
I know there is 5V and GND in the Midi section that will provide power weather you use USB power or wallwart.
I am currently at my place of employment, so I am unable to access my resources to advise you which one. I have powered a full external midi controller from this spot, still used the midi section.
Maybe this is a better alternative.