oh my god how
SteamApps/common/Starbound/assets/ships/human/dropshipblocks.png
Replace that with the image I posted above and create a new char
or delete your current char's .shipworld (Put all the stuff in your ship into your inv first) and it'll regen a new one.
Bam, you now have access to the exterior of your ship. Do NOT break the tunnel, you can't place background blocks to any area to the side of the tunnel so you have to go up a little.