Chances are that he will meet people on the flight that are going to Antwerp (45 mins)who can:
a) Show him the hourly bus to Antwerp and return;
b) give him a ride.
Antwerp has late Shachris minyonim, kosher supermarkets and restaurants. In November, sunrise is around 8 AM!. Can’t daven much earlier than that.
He can visit the bourse (diamond exchange). If it pulls him, he can see the well-known Rebbe, Reb Leibush.
The kever of Reb Itzikel Zatzal is not too far away. Maybe his new-found friends will hire a taxi together and be misspallel at that mokom kodesh.
One thing for sure: he can use his time well if he has the inclination. (In Brussels, there are guided tours; but mostly churches etc.).
BRU airport has a shul.
Fuhr g’zinteheit.
I would love to hear how it worked out. It may help other people.