Is there a way to create ElectricFlow plugin configurations with DSL or ectool?

Yes, each plugin has typically a CreateConfiguration procedure you can invoke directly. Certainly the easiest way.

Also CreateConfiguration generally speaking (it may be slightly different depending on the plugin you have in mind) creates a credential named after the configuration) and a bunch of properties under /plugins//project/ec_plugin_cfgs/. This is obviously more of a "hack" so use cautiously.