The 80 Euro charge has been a bug-bear for a long time. In practice, most people seem to ignore it and I haven't heard of any come-back.
Going north into Dutch airspace doesn't help as you're then in Mandatory Mode S airspace and it's a long way from shore in a microlight.
I can see no problem with routing through Belgian airspace without landing, although that's still technically breaking the rules, nobody will ever know.