Hi Bookworm,
The routing CLN-COA IS available below FL110. I personally don't see a problem with that routing, especially for Antwerp inbounds. They'll have to descend anyway and stay well below the Brussels outbounds. And we still have radar to vector that 747 at 4000' around you...
As said: don't worry about the Dutch airspace, that's delegated to Brussels anyway.
Best thing to do: before you depart, call the Brussels ACC supervisor (+32 2 206 27 22) and make your request. When approved by him, once in the air, ask the UK controller for this routing and tell him this has been approved beforehand.
Good luck!