wow, nice turnaround time there.
ideally the power barrel could be wired internally. the 5v regulator is here:
http://www.digikey.com/product-search/en?keywords=811-2692-nd
it takes 7v to 36v, so it can plug into the 12v rail close to the source, but it’d be better to plug it into whatever the incoming DC power is, which might require a hack. and have the ground attached close to the power jack.
so instead of populating the DC jack you could just wire it direct.