You could always go over-the-top and get him German's #1 Gluten-Free Beer, Schnitzer Braeu!
"German" beers really encompasses a HUGE range of beers, any ideas which particular ones he liked before? Also, do you have lagering equipment (a dedicated fridge or freezer with a custom thermostat)? If you want a dark beer, you're going to have to roast some of your own grains to get the color you want. German yeasts tend to work just fine with sorghum, so that shouldn't be a problem.
Unfortunately saying, "He liked beer while in Germany" is like saying, "He liked the barbeque in the US". Unless we know where he was it's hard to even take a decent guess as to what it was he liked. Because making a nice mustard-sauce pork is going to really disappoint somebody looking for pepper-rubbed brisket.
In all honesty though, no matter what you make him, he'll probably be pretty happy. You could just hope that the Deschutes' Public House has a good GF Beer on-tap at the moment and go up there to pick up a few growlers.