Plan less, ride more. Print out the FJR Assistance list, (get on it if you're not and then print the most recent copy before your trip), then during your trip when you notice your tire(s) are getting close to the wear bars, locate the person on the assistance list near where you want to swap a tire and call them. Find out who's the local go to dealer for tires and make some calls.
The smart thing would be for you to start with a known good performer like the PR2/3 or Me880s, and for everyone in the group to do the same, with fresh tires at the start. But there's always that one guy that comes to the party on tires that have 2k left in them. :blink: Or mounts up some sport tires, being clueless as to how long they are going to last.
Depending on where your trip takes you, and where you think you might be at that 4-7k range you currently get from tires, you might actually consider the CT option. A CT and front PR2/3 will easily go the distances you're talking about with 5k miles to spare, if not more. And that's just the front. The rear CT will go a lot longer. But you don't want to do that change and head out the next day! There is some acclimation time to the CT. Different for each person. For some, it's the end of the block. Others will take a couple of thousand miles to get comfortable with it. Some never do. Regardless of what you choose, you might consider setting your FJR up with a car tire compliant rear brake caliper tension arm so if you get stuck someplace with NO tires in your size, you can actually go the CT route w/o further mods and continue your trip. You can make the new bar yourself for $5 with stuff from the local hardware store. It has zero impact to running a moto tire.