Once you get the center wing section on and after you mount the wings and RIGGING wires to it it will stay in place. Also those 2 cross brace rigging wires that are between the cabne struts will help the cabnes from shifting around. I had the same thoughts when I got to that point. But after I did a mock up of the wings including the "N" struts mounted nothing moved out of its place, even without the rigging wires.

Peter Barth is a master modler and a aerospace engineer working on the Eurofighter. I trust he knows what he designed, after all he also flys these things. He better know what he is doing...... I have all most $6500 in this kit and I don't want it to do anything silly during flight.
But as you know, you can make addtional mods on any kit without hurting it like maybe putting in a spacer where you showed me, a piece of brass tubing would do if that makes you feel better.

Steve