Back in the day, that was standard issue in the ghetto where I worked for a short time. I even managed to get 4 6x9's in the door of a early 90's Firebird without an ounce of fiberglass. At least they all matched.
I know people will want to flame me about being a hack installer but I did EXACTLY what the customer wanted despite how many times I tried to talk him out of it. If some guy walks into your shop and is willing to pay cash (a wad of cash) for what he wants I'm not going to send him away no matter how stupid his request is.