How to keep a TB gelding cool in blazing heat?

My friend brought home her bay TB ex-hurdler gelding last wednesday. He's settled in really well and loves living out with unlimited grass to eat! But lately there's been a heatwave in Southern England which is hopefully leaving, but it might come back. During the heatwave at the weekend when it was the worst, my friend would have to go out and hose down Beau every half an hour. There's a bit of shade at the bottom of the field, but he likes to graze at the top which is closest to her house, where there is also no shade whatsoever. We led him to the shade and left him there, but within ten minutes he'd wandered back to the top. My friend really can't go and hose him down every half an hour to keep him cool, it takes a lot of effort and Beau is VERY strong since he's an ex-racer, and dances a lot when he's sprayed with water, even on a light setting, and my friend obviously can't control a 16hh TB ex-racer on her own, while spraying him. How else can we keep him cool without having to hose him down? Apart from shade as well obviously? Thanks :)