default decoding when content_type not set?

[Scott Turnbull]

I'm reading messages from a several partner brokers who are some of whom are sending JSON in the message body but not setting content_type in the header so Rabbit receives it as application/octet-stream and reads the string as unicode.  I'd like to be able to set a default decoder to unmarshall to JSON if it detects the body as unicode but can't find a way to do it. 

Does anyone have advice for solving this problem?

Thanks.