Firstly is there a way of doing this, as it seems the existing REST broker which is good (when you're dealing with JSON responses) doesn't allow this.
For example I'm trying to query https://docs.microsoft.com/en-us/rest/api/storageservices/blob-service-rest-api and MS just use XML in the response, which annoyingly looks like I have to build my own broker to handle.
Currently this is not possible OOTB at the moment. I see that you logged a feature request for this on ideas.k2.com
I have linked that feature on this post, so that if anyone else runs into this query, they can use the ideas.k2.com site to vote for that feature.