Ah yes the hot leg syndrome.....
I've suffered that in a few places, the worst being in Portugal in 35C heat after a 90 mile thrash through the mountains just to get the engine really warmed up, then having to crawl through city traffic
That was bad enough but then the fan came on!!!!!!!
The only answer to it is movement - I doubt that a shield would do much good but if you succeed let me know how you do it!
Cheers
Andy