Thank you for the reply. If that is my only option, then I'll have to go with it.
The reason I was trying to send it some other method is the Mega cards are in separate boxes and some distance away from each other. So I was trying to minimize the wiring and just send the variable across the USB somehow.
Both Megas are plugged into one computer via USB cables? If that is the case then no, what you want to do can't happen without help from the PC. The two Megas aren't connected to one another in any way that allows them to communicate directly with one another.
It would however be trivially simple to write a sketch in Processing or a program in Python that could be open on the PC. In that case the program could act as a link between the two, receiving Serial data over USB and then communicating that data via USB to the other Arduino.