you have two options.
option 1.
remove the head unit (which you will need to do anyway to connect the blue plug), locate the main power plug (red arrow) and connect to the red wire for constant power, and brown wire for ground. i'm writing this from the top of my head, so please confirm the wires by using a test lamp, and looking at the wire table on the top of the device (yellow arrow).
option 2.
remove the compartment/cd holder under the head unit.
you will find a loose connector, which belong to the optional porsche build in cell phone hands free kit (or something like that).
if i remember correctly, main power is red with green strip, and ground is brown (again, use a test lamp or voltmeter to confirm)
good luck with the install.