I hardwired my GPS & Cellphone chargers under the dash/centre console that leaves the cig lighter available for another gadget.
Could also try mount 2 extra power points on the back of the centre console similare to the E60 5 series has.
http://www.bmwfanatics.co.za/showthread.php?tid=103&highlight=gps
See post 14 for the GPS hardwirreing.. Also did not take pic of finished product.. but the cable comes out the trim to the right of the radio
Cell charger was similar except I have it coming out by the handbrake..