Does one exist? How hard is it to lift it?

Yes - Jason (devonutopia) sells them, and they are a piece of pish to lift by the look of the video

Here is his post about it

Hmm.. reading that thread says you bought one??

i think he means to space the bonnet at the rear so it vents air out. not looked at fabia bonnet but most people use a few washers to raise the rear of the bonnet not sure if fabia design will allow this though

Yarp, several washers and longer bolts if required

Or some large plastic spacers

Jason fitted one to my car at Castle Combe in April, it worked out cheaper too. It makes the bonnet very easy to open and close. Well worth it IMO.

I'm not sure if Jase has any in stock presently, PM him and he might get some sorted for Combe.

To raise the rear of the bonnet not thing that holds it up.

We're talking here about raising up the BACK of the bonnet a bit yes? The method is already mentioned but not sure how effective it is? I bet removing the rubber lining around the edge would allow some air through as well. The only slight concern would be how well the front of the bonnet closes with the back raised up but I would imagine 10mm at the back would not greatly affect the angle at the front when closed.

The Grille is not going to line up with the headlights anymore if the back part of the bonnet is raised.

Dont see the point to this mod. if your car is running too warm then upgrade the cooling system.