Great question....
Couple of tips.... not perfect tips but sometimes all you can do is all you can do....
Start early. As early as you can. Beat the rising of the sun.
Work after the sun starts to go down in the sky. Like around 5:00pm and later. The golden hours. Not a lot cooler but a lot less harsh than working at noon.
Work on the shade side when there's a shade side.
Wear a long sleeved shirt and a sun hat.
Drink lots of liquids. Stay hydrated.
Work smaller sections. This is real helpful when doing any compounding or polishing work.