After fiddling around the whole day trying to get it via the USB Network working I just found out how to connect Eclipse (BB SDK) to the BlackBerry device via WiFi. Just like it is possible at the Nokia N9 and C7.

The connection is not very reliable and quite slow compared to USB, but even better than nothing and wasting a again a whole day booting my desktop again and again until I get the routing across different subnets working. So, I guess I need to stick to WiFi until a unexpected wonder happens.

Thanks for everyone who has tried to help me with my issue! I would have loved to post here a step by step guide how to get this at a ugly Windows 7 host working... but perhaps this honour is reserved for somebody else.