A little known secret - you can easily remove the cog from the lid, with some care and precision, you will not damage either, this is not official procedure, and Jobo did not want you to know this, because of the potential damage to the cog and or lid.
Before doing this consider what has been said above, getting a plug to block the opening in the cog is way simpler....
PROCEED AT YOUR OWN DISCRETION!
take the funnel off.
turn the lid upside down so the cog is pointing down.
place the lid on a ledge of something hard, hard top granite of a kitchen is good. support the other side of the lid with something soft to absorb the blow, like your hip.
Now the lid is held firml between your hip and the edge of a hard counter.
get a flat head screw driver, that is fairly large (a small one will go right through the plastic), and position the top of it at the first indent\curve above the opening in the cog.
Using a mallet\large head hammer and aim to hit the screw driver with one decisive blow.
raise your hip slightly so the lid is angled towards the hard surface, this will divert most of the energy to seam where the cog is lodged in.
hit the screw driver with one precise and decisive blow (not to hard so to blow the whole thing to bits) but enough to pop the cog out.
The cog will pop out and fall to the ground. The lid is now an inversion lid, and you will need to get the red membrane rubber cap.