That way works, however plugin is not necessary.I tried battlefield 3 in xex format and gave me an error. Installed the disc swap files and loaded up perfect. No it does not need to be in GOD format. I read in a another website that you would have to install the HD content manually in the xbox hard drive to work the best because everytime you load the game it will ask to install the HD content download.
W/O disk swap:
1) can extract Disc 1 to xex format, copy the only large file (which is the HD content) to your content/0000000000000000/(Bf3 id)/ folder.
2)Extract disc 2 to GOD format, and copy it over.
Then you should be good to go.