Make sure flag rules are on full, and then there has to be a huge crash. I've only seen it offline because online we don't run the server with full flag rules, but I don't see a reason why it shouldn't work online too. Try it, and let us know if it works.
Yes, I believe it works the same as rFactor. The admin can type throwyellow to activate it. ( I think you can follow it with the number of laps as well, e.g. throwyellow 2 )
But I am not 100% sure of the command - it is a while since I tried it, but it DID work, so assuming Reiza have left it in 1.20 it should still work.
And IIRC you can also use a command to go green next lap - I think it is pullyellow but again I'm not 100% sure.
So for example you could throwyellow4, then after 2 laps you can cut short the yellow period by typing pullyellow and go racing again on the next lap.