1) That URL is along the lines of what I had figured out myself earlier - but note that he does it with "file" and multiplies by 512, while I did it with "fdisk" and multiplied by 65536 (after subtracting 1).
2) "kpartx" looks interesting, but it seems to me that all kpartx does for you is avoids having to fiddle with offsets - i.e., it does that part for you, including the multiplication. You still do the mounting (with -o loop) yourself.
And some folks need to stop being fanboys and see the forest behind the trees.
(One of the best lines I've seen on this board lately)