Blimey.
I don't stare, I scan.
Instruments, road immediately in front, sweep to horizon, left mirror, road in front, sweep to horizon, right mirror (avoids having to tell the biker that "sorry mate, I didn't see you"), road in front, sweep to horizon, rear mirror.
Should take no more than 10 seconds.
If you're feeling tired and *cannot* stop, commentate the drive to yourself a la IAM standards.
"Maintaining speed of XX miles per hour, silver Mondeo approaching rear, junction with traffic lights ahead, filter lane may mean split priorities, cyclist ahead so I need to pull out, mirror and shoulder check beforehand, indicate yadda yadda"
Or you could stop, get out, walk around, take a piss and stretch your legs.
Or, instead, you could eat crunchy things.