I am not familiar with MQ...
But many utilities support a continuation character. For example, in TSO, it is a plus sign (or minus sign). Add the continuation character at the end of the line and the utility knows to read the next line and append it to this line. Add a continuation character at the end of each line until you complete the entire logical record.
I googled for 'mq continuation character' and found this:
When you are using the command interpreter runmqsc to enter administration commands, a + at the end of a line indicates that the next line is a continuation. Ensure that there is a space between the last parameter and the continuation character.
I am not sure if that is what you are referring to.