Thank you to all who replied. Based on your advice I'm going to run
the #6 solid bare wire back to the main panel. I figure the #6 will
be easier to push up/down the short length of conduit from the ground
to the service elbow. I wish either myself, my dad, or the building
inspector would have caught the mistake earlier, since I have to
re-dig my trenches! Oh well, our clay was hard to dig the first time,
but at least it is also pretty hard to tamp well, so the digging will
go easier this time! I can't go through the house or garage since
it's all finished (which coincidentally is the same reason I needed
the subpanel in the first place).

Thanks again,
Korey