I just installed mine today. I don't know if it's frowned upon, but I saw enough places online talk about poking a hole in the existing membrane and then forcing the power wire through, after taping it to something small/thin like a metal coat hanger. I only ran 8 gauge and it wasn't that hard to pull.

This is my first car audio install, and the only thing that I wish I would have read, is that the clips that hold the factory wiring come off so you can run your RCA/Power/remote cable through. This will get them out of the way when and keep them secured. I found out the hard way and drove a screw through the remote bass control cable, luckily it was only the remote and not the power cable. I found this out after reinstalling all the trim on the driver side.