Hate to blow my own trumpet but I'm gonna have to here... I rode my DRZ Surrey, England to Cape Town, South Africa (
East Africa Route), 4 months in the saddle doing high mileage gives me some experience.
I'd suggest something I've learned since the trip, set yourself a goal... 60 minutes, 60 miles, or just the name of a town... and ride at a set speed (if doing motorway), or at a set
style for that period. Stop have a break and reward yourself once you get there.
Stretch out good (lots of emphasis on this). And then set your next goal.
Also, just because there's only 20/10/5 miles left, it doesn't mean you don't need a break (I still haven't mastered this fully). I find I begin to make stupid mistakes and errors in judgement as I get knackered. It's always advisable "that last little bit" isn't worth not taking a break if you feel you just need it.
Some years ago, riding back from the Pyrenees on one of my DRZs I cained the length of france in about 36 hours with a little sleep on the ground at a service station, and then as night fell and the ferry hit Dover (and 50 miles left) and not having any tail-light or headlight dipped beam, I carried on in the dark... like an idiot full beam on, right hand gently on the brake so the tail-light would show. I was exhausted and no urgency to get home. I would have benefited just from camping up the night and making my last 50 miles home in daylight. I got home a train-wreck... brakes on the bike knackered, and cramp in my wrist from holding the throttle open (and brake applied) for so long. Totally worthless. Plus I just ended up spending the next few days lounging around at home anyhow wishing I was still on my bike.