Automatic SiteID Creation at record time?

I’m trying to start getting analytics on a platform which will host thousands of sites, and would like to avoid having to keep two databases of Site IDs in sync; rather, I’d like to configure Piwik to automagically record a “new” Site ID as a real site instead of 400ing.

I’d have sworn that I could do this in Piwik about a year ago, but have no actual evidence at present.

https://forum.matomo.org/t/automatic-creation-of-websites-in-piwik/1194 is a couple of years old, and mentions that this is an interesting idea (which means that it probably wasn’t possible then).

https://forum.matomo.org/t/any-way-to-use-piwik-tracking-without-side-id-in-the-code-e-g-automatically-add-a-website/18506
very strongly suggests that it has never worked, but that there may have been ways to “cheat” it into working.

Is this a feature that is under consideration or development? Or, is there a setting somewhere that I (along with, apparently, several others) am missing?