You can create the user by calling the NBWS and calling the method "CreatePublicKeyAdminUserConfiguration"
However it would appear you cannot load a key in automatically. (I do not see a web method for that). I will check with engineering but I would imagine it would have to be an enhancement request to write a web method for that.
--Shaun Roberts Principal Engineer, CX firstname.lastname@example.org
Unfortunately, it looks like this is not possible in 2.3.X. (That is you can create the user but the fields you need to use to configure that user properly do not appear to be exposed to the Northbound Web Service).
It looks like something that will be fixed in a future release of Process Orchestrator.