The problem with purging with CO2 is that it won't last because the barrel breathes, and oxygen will work its way in. I don't know how quickly that will occur but it doesn't seem worth risking. But its only 10 gals if you think its worth the risk. Barrels intentionally slightly oxidize whatever is put in them and they allow for evaporation - this will happen more quickly if the barrel is not full. It may not be enough time to pick up the good bourbon/oak qualities before the beer becomes too oxidized. Looking online, your price seems like 1/10th what used 55gal bourbon barrels are going for. I would really like to get one for 18 bucks!
"Did you ever kick a woman in the midsection while she was wearing a whalebone corset? I nearly broke my great toe. I never had such a painful experience." -Egbert Souse(W.C.Fields)