Does this even work on the wireless interface on a mbp? The driver used to prevent you from setting the MAC addr to anything you wanted, vs the ethernet driver for the wired interface that lets you play with it freely.
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -z
Then you can change MAC-address: ifconfig en0 ether aa:aa:aa:aa:aa:aa