I was the one who requested the original feature request back in 2019 from SAG for support to MQIIH headers but it seems they did not make any headway on it. You can do the same thing i did by using the IBM MQ classes to create a Java service to inject the needed headers in to the message for sending outbound messages to the MQ Queue.
For MQIIH i used below code to inject the headers. You might have to do the same for MQRFH2 headers. Look at this Stack overflow question.
MQIIH IIHeader=new MQIIH();
IIHeader.setFormat("MQIMSVS");
IIHeader.setReplyToFormat("MQIMSVS");
IIHeader.setAuthenticator(password);
IIHeader.setSecurityScope(securityScope.charAt(0));
IIHeader.setCommitMode(commitMode.charAt(0));
MQHeaderList headers=new MQHeaderList();
headers.add(IIHeader);
#Adapters-and-E-Standards#webMethods#Integration-Server-and-ESB