I thought about this last night.
I figured if you remove the current radiator and installed a smaller one, then completely removed the coolant thermostat from the cooling line. Then installed a cooling fan on the radiator, then the fan could act as a thermostat of sorts, and the engine would get up to operating temperature and stay there for longer and the limiter would be the electric cooling fan.
This way you could do a much more substantial partial grille block having only say a hole the size of a 12 inch laserdisc to open up.
Could even, depending upon the amount of space in the engine bay, do a slant-downwards radiator, which picks up air from underneath the front bumper and grille.
Then with one of these:
12V Thermostat Temperature Controller LCD W Regulator Sensor Control Incubate | eBay
In control of a "lip" which opens up and lets fresh air into the engine bay from
underneath the front bumper bar, and closes when no longer needed. Controlled by a
Obviously some aluminium cowling to direct airflow into the radiator would be required, from underneath the front bumper.
Another idea Is to use water mist cooling to spray (using windscreen wiper sprays) onto the radiator and having a complete radiator grille block installed, the water evaporates (make sure it doesn't get onto the engine block or manifold!) and removes any heat from the engine.
Controlled by the same above 12v thermostat.
There would need to be a level gauge telling you when you gotta refill with water. I suggest installing a large water container in the boot of your car, possibly 40 liters in size.
Obviously a large amount of on-board water would be required at all times.