Absolutely the best solution to a rear impact scenario requires good speed capability, constant awareness, and one piece of specialty equipment.
First you want to be traveling, as closely as possible, to the speed of the approaching vehicle.
Second you must have an awareness as to the velocity, angle, mass and surface composition of the vehicle. Sets of 4 mirrors, or more, recommended, if possible, arrange into a stereoscopic, full 3D configuration.
Thirdly, and most importantly, the one piece of specialty equipment! "Cyclists Downunder", (based, possibly, in Australia?), has begun marketing their "Octopi" line of cyclewear.
Just make sure that you are struck squarely from behind. If you are about to be hit, quickly swerve and position yourself directly towards the center of the vehicle, the car should knock the bicycle from under you and you should roll gracefully onto the hood and, or, windshield, where the Octopi suction cups should keep you safely secured. (Tip: As soon as you get stuck to the vehicle, rip off one, or both windshield wipers! Some drivers will use them to try to knock you off. You can also beat them on the roof to get the drivers attention, in case he is sleeping, or just doesn't notice you.) Hopefully the car will come to a gentle stop and you can then safely get off. Much safer than rolling down the road at 30 mph or bouncing over the roof and landing, "who knows where"! (Tip: Please do not anger, or insult, the driver! You will probably need their help getting unstuck from the car!)
Warning! Speed is important! 20 mph bike speed is optimal to be hit by a 30 mph car.
Slower can result in fairly severe injuries.
Faster and you might not be bounced onto the top of the car, you might have to jump backwards, timing is critical! Warning! Be careful, some a__hole drivers will approach like they are going to hit you, then ... slow down, just before impact. If not aware you might jump, and miss, ... then where would you be? ... Embarrassed! ... ???
Large trucks can be very tricky. Most don't have a nice hood to get stuck to.
1. Ideally, you must be going 10 mph slower than the truck.
2. Timing is critical, you must jump straight up just as you are being run over.
3. You must hit the windshield squarely, with enough body, to stick. Grills-radiators don't work well with suction cups!
This is a skill! Like any skill it requires practice. You should have a friend try to run you down, a few times, just so you can get good at being safer.
Oh, ... Make sure you have a good supply of bikes handy.
P.S. Be prepared for being hit by the, proverbial, "Redneck Pickup". Keep an Armageddon bag handy, on your bike. Recommend couple bottles of water, sun screen, some granola bars, "Space blanket" ... anything you might need in case they drive around with you stuck to their hood, for a few days.
Disclaimer! You must read "Epitaphs of the Downunder Cyclists", before attempting this "solution"!!!