It really is not available. The check for the preset parameter is hard-coded to always throw the exception. The reason behind this is that the ReST API only know how to import / pre-construct the structure of a default site, and it offers no extensoin point to allow adding an import for an arbitrary preset. Alfresco being Alfresco, they opted for the easiest solution that would allow them to release a new feature: hard-disallowing sensible parameters to be used and not caring for people that extend Alfresco.
It should be noted that one can always try to enhance their implementation by providing a pull request on GitHub. That might be the most likely way to make their minimal viable features into usable ones these days.