The problem is that the unit locks out most navigation functions when the GPS senses the car is moving, so it is not as easy as just bypassing the e-brake wire. Here's what you do: First, you need to ground the ebrake wire. Don't hook it up to the ebrake switch, but ground it to the same location the radio is grounded to (or you could find a different ground location, but this is easiest). Second, pull the harness out of the radio. You'll notice there is one open wire slot next to the ground wire (in the top left of the plug, depending on how you are looking at it). You need to stick a wire into this location and ground it, too. The easiest way to do this is to pull out another wire from the harness you don't use (typically, either the cellular mute wire or the power antenna control wire) and just stick the wire connector into the open wire location. After grounding the ebrake wire and the harness wire, you are all set!
This will give you full navigation control while your car is moving - and if you have XM, it will also allow you to look at sports scores, etc. In no way am I condoning people using their navigation while driving, I just find it annoying every feature is locked out when I am in the passenger seat and want to play around with the system.