You have two main options. The first is something like the Hasa Liquidator which uses the pressure difference across the filter and pump to inject liquid chlorine. The second is a Peristaltic metering pump which injects liquid chlorine from a tank into the return line. Search for "Stenner" on the forum to get more information.
The downside to both the liquidator and stenner is that you are still carrying bottles of bleach/chlorine. The only way to eliminate that is to go with a salt water chlorine generator. Now, they come with their own set of issues so take the winter and research all of the options. Don't take my word or the word of anyone anyone else, do your research and see what works for your situation. But please, don';t stop by the local pool store and ask what they think.