Allow for handling of arbitrary HTTP status codes at the APICast level

When creating/updating an integration the option exists in porta to setup handing for 4 "GATEWAY RESPONSE" codes.

A customer has requested handling for additional codes including specifically 400 Bad Request

We are trying to handle 400 Bad Request in 3Scale gateway level but unfortunately we are not sure how can we handle this.
In our 3Scale environment we already handled custom error codes, and its working fine.
Example:
---------------

{
    "status": "Failure",
    "errorCode": 8429,
    "message": "Usage limit exceeded"
} 

403, 404, 429 HTTP error codes by default present.
How can we configure more HTTP error codes in gateway level?
Please find the attached.