boggydew:
Usually when I do this I declare
HardwareSerial * mySerial; as a private variable in the class definition (usually found in the .h file).Then I pass a pointer in my sketch, such as myUSBHostObject.init(&Serial1) or some such, then modify the .cpp code like USBHost::init(HardwareSerial * serial){ mySerial = serial}. Then I can print to serial monitor with mySerial->println();
That's a perfect application for Polymorphism. Pass a pointer to a object of the Stream class. Or, if you're only printing to it (and not also reading from it), pass a pointer to an object of the Print class. Then, your code will work with ANY object that inherits from those classes.