dieselV6

I have ventectomized all 3 Skodas I had and most of the time fill up till diesel settles just below the metal lip of the filler neck. Expansion has never been a problem, I suspect the plastic tank expands as much as diesel. It is more of a petrol issue, but this mod is unworkable, illegal and dangerous for petrols, while providing nice extra capacity for diesels.
 
You can keep the nozzle almost all the way in, but you still need to fill the last 5-7 litres slowly, while diesel fuel in the tank foams off. No way around this other than finding a station dispensing fuel with anti-foaming additives. Non-foaming fuel takes only about 1min shorter though.
 
Nozzle all the way in (as in pressed in) results in nozzle cutting off at full flow anyway, at least on my cars, so I keep it about 1/2in from the full in position. Ventectomy is still much safer against spills than pressing the vent valve, as the nozzle 1/2in from max is still quite deep and will cut off once fuel hits it back.
 
On the Superb, you can access the vent valve under rear wheel well liner I think, though I might be wrong on this as the last time I looked there was 8+ years ago. Flat screwdriver to press a catch and push out, then remove the valve , put the plastic assembly minus the valve back together and push it back in. Really simple.