Hi Max,
the easiest way would be to use the cloud edition, that includes an agent with auto registration features that does exactly what you want 
Otherwise you can just trigger a powershell script on the monitored host, read its local hostname and create the host via the rest api. Alternatively the software deployment could trigger the script, if you can give it the hostname of the target host.
An example is e.g. this, but there are several examples in this forum.
In the checkmk help (lower left) in the checkmk gui there is the complete API documentation.