Sorry, but you have to do all the faces. Its a script that does the work for you.
However, there are tricks…and somewhere maybe in the posts of october I answered this.
Unwrap the faces you want, etc. pin them, then grab them and move them up to the top above the square in the image editor.
Now select all the other faces , or select all and unwrap them… your chosen faces should be fine where they are, and the others should be in a jumble on the square.
Now use the b key and box select all the unwanted faces. Now press s and scale them to a dot. and move them to a corner in the square.
Now grab the chosen faces and drag them back to the square however you want them. Now run the script.
Just ignore the tiny dot in the corner. YOu can scale them to the size of one vert! Pretty cool.
Hope that helps
ps. I noted that some people just do a screen print of the uvimage editor view and save it to work on. I have never tried it. I prefer the way above because it keeps it to the size I choose when I save the map.