yea the straw trick is only good for like the smaller wires.
I just used it with the wires for my leds. and just shoved my amp wire through later.
But hope you get it!!!

 

i wish that scion knowing that people like us will add sytems to our cars hence the reason of the outputs on the premium radio....would add like a blank rubber grommet to the firewall that was just for the power wire to run through ive seen them on many cars that i have worked on...