Ok, just to reply to my own question, maybe someone will be in the same situation:
While I wasn't able to read the connector's configuration to get the SDM (default) connection parameters, I switched from using the default 'SOAP Call' operator (which would need explicitely the connection parameters) to using the 'SD Web Service Operation' operator (part of the CA Service Desk group or Operators) which is quite similar, but has the advantage of performing the SD Soap call guarded in a login/logoff sequence, reading the default connector's configuration for these steps.
This way, I retained the flexibility of the raw SOAP web service call and didn't have to explicitely enter the connection parameters in the operator or process.