This is a tool to easily create and post a switcharoo to /r/switcharoo/new. It uses api.reddit.com to get the link of the latest post there and inputs it into the comment field, then asks you for some info about the comment chain. It opens a new url, and bam! There's your switcharoo post.
Go here. Then permalink to the comment that you'd like reply to, and click that bookmark. Follow the instructions, and congrats! You've made a switcharoo!
mrcoles' bookmarklet converter helped me with testing this. I also used it and its syntax to make my bookmarklet loader.