Originally Posted by dj_jay_smith

Yes this is a right pain at the moment. It is still open, but difficult to access.

If you come from the West (Wiesbaden, Mainz, Cologne) then you need to take the exit for T2 as you did, but as you can't go round the roundabout then follow the road towards the Terminal. At the first set of lights you need to be in the far left lane, and then you can actually make a U-Turn.
There are normally lots of people doing this, especially Taxi drivers!
Then follow the road back and go on the roundabout (left lane again), and then you can come off the roundabout for the Esso station.

There is also a Shell (?) on the Airport ring towards the west. But I have not been there, and it is more awkward to get to from the Autobahn.