Webhook Response Mapping for HTTP Response Code

I'm building out a custom integration passing data from Marketo to a Salesforce custom object using Marketo WebHooks and Salesforce's REST API. I've successfully built the integration but want to add a small amount of error handling by capturing the HTTP Response Code from the WebHook call out. I can then use the captured response code to determine a success or failure but I'm not able to figure out how to use the WebHook response mappings to retrieve the HTTP Status Code.

Is Marketo's Response Mapping limited to the JSON Response that the HTTP delivers back? Is there any way to get at the WebHook status code? Attached is a screenshot of a successful webhook execution. I'd like to capture the "204".

Thanks!

-Ben