You sure can. I think there are a few threads on the topic on this site, but basically you can just take your bottling wand and insert it into your tap faucet (or picinic faucet). Purge most of the gas out of your keg to reduce foaming, and fill your bottle. When you pull your wand out, there will be some headspace, so it is important to remove the bottling wand from the faucet and then fill the bottle the rest of the way so that foam comes out of the top. That will remove most if not all oxygen from the bottle. Cap immediately. The bottle should stay carbed for weeks or even months.