Haven't done it, but it shouldn't be difficult to do. With a metal straw, you could just use a drill press and drill out the lid to the exact diameter of the straw to insure a nice snug fit. If air is needed, you could add an additional pin hole in the lid. If the straw doesn't happen to stick out from your bottle very far, you could always add a short length of tubing to it, for hands free drinking.
If the aluminum straw doesn't work out, you could always just find a piece of aluminum tubing that's a snug fit inside your hydration tube, and make your own straw...
Got tons of 7-11s here in California. If I can remember, I'll stop for a Slurpee and see if they still sell those metal straws. Slurpee's are so good, I drink them even in the winter... If they do, I'll send one your way.
I'm interested in your MYOG pack. Do you have any additional info on it? better pics? I was thinking of doing something similar. Attaching two 1L bottles to the shoulder straps. I'm also interested in making it as ventilated as possible, which yours seems to be?