No idea about the Fanatec but with a G27 there are three different kinds of shifting schemes, I can only remember the one I used but it basically used a button to double the six speeds. So you'd start off in 1st, work your way through to 6th, then press a button and shift back into the 1st position, which then became 7th. There was one super complicated version which gave you four different shifter layouts which mimicked how the Scania system works, I think.
There's a demo for ETS2, by the way, it's pretty fun but I don't think I'd buy it.