Read this thread. I and others discuss the BMW rack that goes in the eye sockets. It can be very easily removed in less than a minute and access to trunk is not an issue as the rack swings back to allow opening of both upper and lower trunk gates.
http://www.bimmerfest.com/forums/sho...818&highlight=
Also, while the rack is badged by BMW, it's actually made by Atera Strada. Check out their website here. I think they make an extension for a third bike.
http://www.chwhite.btinternet.co.uk/...ra_strada.html