Ok, test-race is over (SO6R / LX6 in open config mode)
Blue Flags:
I have to say, blue flags are working really good.
I guess the system is a bit more sophisticated than the one I suggested.
All the drivers have been in teamspeak, so I now have a fairly good overview of what peaople were thinking about it. Some said, blue flags were near perfect. Others said (and I feel the same) they are shown a little bit too early. Nevertheless, the LX6 is not the fastest car in game, so I guess that'll be ok.
It also seems to depend on the track. We were having some fun in the Blackwood carpark after the race, and blue flags were shown much later there. I guess this happens, because the new blue flags are only shown when the lapper is within a certain angle behind the car you're driving (which is a good thing). So: the curvier the track, the later the flags are shown. They still felt to be "in time".
To cut a long story short:
We like it.
I think it really is the best you can expect from a workaround like that.
Thank you very much!