When we first set up the flexfuel stuff we were using ~E98 from Alcotane and just pouring it into the tank while watching the ethanol content on the Link software to try and get it to the right level - as seen in this vid from the first time we tested the sensor:
http://www.youtube.com/watch?v=5zs9C6Xf8-s
As per earlier posts Alcotane have been difficult to get supply from so the latest bunch was from Kerry Halligan in Palmy which is Sucrogen E85 - which makes it a bit harder to get the ethanol percentage up if you are using pump gas as well as the ethanol concentration is clearly not so great, and which is why the car was mainly running ~E60 at Manfeild as opposed to E85.... that is basically what it ended up as after pouring 40 litres of E85 into tank which had a little E20 (or thereabouts) still lurking within from previous mixes.
So in short, the mixing is done in the tank by pouring "stuff" in - which may be ethanol, or petrol, or a bit of a mongrel blend of the stuff