Sounds like you are really worried about this. I think there's a bit about parenting which does involve the wait / worry / wait / worry syndrome, unfortunately.

Since it appears you are unable to confine him to the naughty step until conformance - and assuming your line of argument cuts no ice - how about bribery? Sending him a few days later in CE via a Reward Flight Saver?

If all else fails, the reality is that health care in Germany is at least as good as the UK, and the flight is so short that I doubt there will be a problem there either. They are also very familiar with student japes out there too. Security is quite used to dealing with people with lots of metal in them, so I'm not sure that's going to stop him. And make sure his phone is fully charged!