I'm not too sure how to get them to pop up. But I think under the rules tab if you press "Add A Rule" you can add "Display a Message." Then pressing "Edit" should let you write what ever you want. Then once the session is started the message should pop up. Now there is a way to get them to pop up at times and locations with triggers, but I dont know how to work those.
And now that I have re-railed this topic, lets derail it again.
Dragonharh, while I do appreciate your efforts and your work, you dont need to plug* your route and where its going to be available all the time. Not saying that you do, but that last little bit about what your working on might not have been necessary. Also, this topic might have been better in the "Surveyors, Operators, and Engineers" as thats what it pertains too.
And lastly Dragonharh, I'd say go with the DLS for your route. That way other users can make sessions for it, namely multiplayer sessions for it and enjoy your route in that aspect.
*Plug - Advertise some thing at every possible moment.