How to set flight plans without the navigation menus?

Wondering what methods people are using to set up flightplans inside their fmc's manually without the use of the in-game navigation menu. Since the navigation data is not up to date, there is nowhere to plan routes accordingly.

Are you just setting up the route in the navigation menu, memorizing it, deleting it, then inputting it from memory?

What are some good approaches to this for people who want to input their flight plans manually?

Thanks