Hi Michael - I also made the switch from ON24 to WebEx. I just setup and tested using the same 'WebEx: Register' Cloud Connector with two webinars, choosing to source the WebEx Event ID dynamically. This way, you only need to setup the Cloud Connector once. Then, for each registration form per webinar in Eloqua, include the 'Post Data to Server' processing step and use the same URL from the instructions in the Cloud Connector configuration.
You'll want to reference Event / Webinar Cloud Apps - Registering Dynamically as well as Form Tools - Running a Cloud Connector via Form Processing Step (as Ashok kumar mentioned above).