I just think the stewards have leeway. They are allowed by the regs to give additional instructions to the teams prior to the race, and there's no reason I can think of that they can't say that they "will use the FFM readings solely to determine if a driver is exceeding the allowed fuel flow limit". Then they are able to hand out 10-second drive throughs and if the team doesn't do the drive through they can be black flagged. It puts Red Bull in the position of having to defend their defiance of the stewards rather than if they did or did not meet the letter of the regs.
On the short term this works. However, on the longer term red bull could file in lawsuits against the fia due possible abusive use and not following usual procedures. The earlier announcement by the fia that any possible infringement towards fuel usage will be handled after the race doesn't help. And the fia still holds end-responsibility, even if the stewards are the ones ordering the black flag.
You have to understand that these things are very tricky when it comes down to juristic fight: any hint of procedural errors can be enough to undermine everything the fia uses in its defence. Even if the court of appeal puts the fia in its right, red bull can still evoke this at the civil court. Furthermore, if it turns out that the fia was wrong, then red bull will be forced to go to the civil court in any case. There's no appeal possible towards a black flag within the juristiction of the fia, so they'll have to do that.
I just think the stewards have leeway. They are allowed by the regs to give additional instructions to the teams prior to the race, and there's no reason I can think of that they can't say that they "will use the FFM readings solely to determine if a driver is exceeding the allowed fuel flow limit".
But how far does that leeway stretches. I could be wrong, but I suspect that is limited to safety reasons. You can't stretch safety reasons that far. Again, I could be wrong. We also have the precedence that technical directives forfill any technical instructions prior to the race.
I'm trying to find any ruling about the specifics of the stewards role, but can't find it. Anybody knows where?