Many thanks for your support. Finally I ended up with building my own g_ether.ko from source. Since the CodeSourcery toolchain didn't work for me, I switched to Ubuntu gnu-arm-toolchain. And voilá, I could load the module and connect to my Kobo Touch via USB network.
I am still wondering why I get 568 from uname and Tony gets 580. I am sure I have a Kobo Touch including Wifi. Maybe there are different hardware models on the market. I bought my one (Model: N905) in Germany.
Since I am now "familiar" with the gnu-arm toolchain I am looking forward to get multitouch running. As far as I know Nook Simple Touch is also based on Neonode zForce touch interface, and for this one some multitouch tweaks exist. I had a first look into the sources (neonode.c) and it shouldn't be too complicated to report more than one touch event at the same time.