Thanks @vmile. I did take it apart. I think I would have to upgrade. Or can I just plug off? When time permits, I will have to take another gander at it.
The flame check valve joins the gas inlet line to the manifold. Disconnect the gas line from the flame check valve, then unscrew the flame check valve from the manifold.
You then need a male/male adapter to join the gas line to the manifold. No need to upgrade the manifold, just need to get the correct male/male adapter.
The Flame check button then sits nice and flat on the control cover.
The valves seem to fail over time (the button does not stay down), and Weber do not offer a replacement part as far as I can see. My main gasser is a 5000, and the flame check actually failed on it last month, so I have just done the 'mod'. I also have another 5000 as a spare, and when I bought that one, the owner told me that the Flame check did not work, but it was easy to work around, "just sit half a brick on it".
That actually does work, but it's ugly.........