Pushing the beer out with a racking cane and CO2 would be much easier and also much safer. One thing that would concern me is how you plan to fasten the screw eye to the exposed rafter. It's not good practice to use a screw eye this way for an overhead suspended load and this is even more important when that load is a glass carboy. It would be better to use a saddle type bracket with a bolt through it horizontally. This way the stress would be carried by the shear strength of the bolt and not by only the wood screw threads of the screw eye. Pulling straight down on a screw eye like that is not a lot different than pulling straight out on a nail. More than likely, the screw eye would hold the load, but if it should happen to fail, the result could be catastrophic. It would also be a good idea to spread the load over two or more of the ceiling joists. You could do this with a piece of plywood. The plywood would also allow you to use an eye bolt, nut and washer instead of a screw eye which would be a much safer method.
