Returning errors and headers from the RequestStreamHandler lambda interface

Hello,
We managed to setup response streaming through Cloudfront from a Java lambda by implementing the RequestStreamHandler and connecting a function url with invokeMode: InvokeMode.RESPONSE_STREAM. It works very wel, but there seems to be no way to return any errors or alternate http codes or headers with the response stream, which results in empty http 200 responses for illegal requests. Is there a way to return this response information from the RequestStreamHandler and if not, is there a roadmap to implement this? Also a workaround to return http errors through cloudfront on empty responses would suffice for now.