When installing OpenAM through UI or CLI, there is no possibility to entirely skip the creation of a user store (datastore). The only workaround appears to be to delete the datastore with ssoadm/amster post-install.
This is quite inconvenient if using external configuration store and no datastore exists:
If no USERSTORE_ are used, the configurator will need a "people" suffix and try to write a demo user to the configuration store.
If USERSTORE_ settings are used, they must point to a valid LDAP server, presumably the config store (where else??), and a valid USERSTORE_SUFFIX that can be written to.
It should be possible to install and run OpenAM without any configured user stores.