Actually there's an option called 'Aktive Sitzbelueftung' (Active Seat Ventilation) on page 16 in the German X5 Accesory cataloge (
http://www.janixworld.com/x5/misc/GY_X5_Acc_2004.pdf ), however it doesn't list a price (only on request).
I will be in Germany next week visiting BMW AG (one of our customers) and see if I can get any more details ....
- Jan