How to define multiple file downloads for a single library in drush make
You are close, you should use destination instead:

libraries[jquery-json-min][download][type] = "file"
libraries[jquery-json-min][download][url] = "http://jquery-json.googlecode.com/files/jquery.json-2.3.min.js"
libraries[jquery-json-min][download][sha1] = "2a4615b93c65dd50f92117c570121035a0327fee"
libraries[jquery-json-min][destination] = "libraries/jquery-json"