.....either line yourself up for a last minute cancellation - be ready to get the bike there quickly.
Or at least book it in, I think you'll be covered if it goes outside of the warrantee mileage if its booked in for its service and you can't get it there because of a long waiting list.
I'm not sure how much room there is to go over the mileage / age - maybe 10%? without getting into discussions around booking times.
The other option is of course to book it up earlier next time!!!
Tim