Changes

Take a train or bus 21 to Brussels International Airport. There are many exits at the airport. You can find one and start hitching from where cars pay their parking-ticket. A bit further down the road towards the motorway you'll find a Shell service station. Most cars here stay around the airport, but you may have luck. A final suggestion is to keep on walking along the side-road until it joins with the motorway. Cars go relatively slow here and there is plenty of room for a vehicle to pull over.