Build yourself an extremely elaborate system of nozzles, tubes, and pumps to spray Starsan in the bottles for two minutes, being sure to spray for NO LONGER THAN 30 SECONDS at a time. Make sure the Starsan is at room temperature, and the bottles have previously frozen (This is important, I can't stress this enough). You'll want a chamoise (the kind you use to dry your car) to make sure the outside of the bottles are completely dry, because bacteria can travel from the outside of the bottle and back inside, rendering the whole process useless.
In all seriousness, you can dunk them, or you can use a Vinator. I've used both, they are both effective (I've never had a beer go bad as a result of using a Vinator). Don't buy more equipment if you don't have to. Don't have a bottle tree? Use your dishwasher rack, or just set them on a clean towel on the counter. Pour out the Starsan and fill with beer. A little bit of Starsan in the bottle isn't going to hurt anything.
RDWHAHB. Cheers.