Can you visit him and offer up a cool bath? One summer when it was hot back at old house we sponged our girls with cold water throughout the day.
Just thinking also, will he need fly rug or fly spray? I know it's early in the season but those nasty horse flies seem to hatch out once the temps come up. We thankfully don't have that problem here! It never gets that hot. I am sure he'll be fine though, so long as he has his water etc, he might drink more? Maybe give an extra bucket?
Has he got any kind of shade at all? Even just a tree to stand under? I honestly wouldn’t worry too much, just make sure he’s got plenty of water.
I'm sure he will be fine, Belle was ok tonight and she's still quite fluffy, it's been 25 degrees here today too. She is in a paddock with no shade too.No shade in this field, I'm planning on getting him a gazebo for summer wasn't expecting temps so warm so quickly!