Inspired by http://www.thingiverse.com/thing:942115 from chrisdug (many thanks!). Printing ABS and PLA was never a problem for my printer. But printing flexible materials as Soft PLA from Orbitech was not possible if the print goes more than 45 minutes! The extruder then is around 40 °Celsius and the filament blocks in the worm-drive. With this easy and powerful solution the problem is gone. The new extruder fan is turning on every time the hotend-fan (not the nozzle-fan) is running. I use the fan directly on printers body housing without destroying any structure. Works like a charm. See the instruction page for more details.See the pictures in reverse order: