Via the "Balloon flight input form" available on AIM-Meteo Briefing, balloonists can notify a balloon flight to Brussels Brussels Flight Information Service (FIS).
Mind that this "Ballooning flight notification" is not a replacement for a flight plan.
Balloonists still need to file a proper flight plan when crossing national borders.

When a balloon flight is not taking place the flight can be cancelled via the "Balloon flight cancellation form".

AIM Briefing

Annual report 2017  
Video: Aeronautical information - Essential information