Yes, upload the route first, then upload the session anytime after that. Make an announcement in Freeware Announcements and list the session and mention it is an integral part of the route and mention why that is. In my case I used Driver Speed Rule to control the variable speed limits and made a Base Session then used that to make the other sessions. You can also make reference to the need to download the session in "Edit Route" menu item and give it a nice thumbnail while you are there.
cheers
Graeme