If its a paraffin waxed barrel, there is almost certainly no use for it in brewing a wild beer. The bugs will not be able to enter and take up residence in the wood. No air will exchange through the wood. And, no flavor would be imparted. I believe your only option would be to dismantle the barrel completely, scrape the wax from inside of the barrel, sand down a layer (at least 1/8 inch?), and then reassemble the barrel.
This would render the barrel closer to a new oak barrel, which would result in way more oak tannins entering your beer than desired. You would likely have to age some dummy beer in the barrel for a time, and then dump it and go through a series of washes with boiling water (and steam if you can).
If I were you, I'd call it a lesson learned and get a new barrel. This time look for a used barrel (preferably wine). If you get a liquor barrel, and don't want too much of the liquor flavor to be imparted, I would fill the barrel with water and let it soak for a few weeks occasionally changing the water.