Good question and thanks for posting!
There are a couple of ways you could approach this. One is to build out the tar.bz2 package, then convert/transmute it to the .conda format using conda-package-handling (there’s an example in the README ). The other option is to set the “Output Type” to conda_v2 in meta.yaml.
As you’ve found, neither method is well documented, so we’re working on improving that. Also, there’s a Conda enhancement proposal in review to improve this functionality overall, if you’d like to comment or review.
Thanks again for the post.