As with working on two circulars, I've also written on the topic of working two socks at the same time, in the Summer 2013 issue of Sockupied.
Here's a quick summary of the process: The two socks sit side-by-side on two circular needles.
(My usual stellar photography...)
And you work as follows: across the first half of the first sock (green in the photo), across the first half of the second sock (white in the photo), across the second half of the second sock (white in the photo), across the second half of the first sock (green in the photo).
So once you're cast on, it's simple! No pattern mods required. Just keep track of which side you're on. I tend to use removeable stitch markers or safety pins to keep track of which sock is which - a green marker on the first sock, an orange marker on the second.
(As for casting on, I usually cast them on separately and slip them to two needles in the setup above.
Turning the heel is easy: work them one at a time! Really!
I do know knitters who separate the socks for turning the heel and picking up the gusset stitches. That can make it easier to visualize and set up.
The only tricky bit is the gusset pick up: it has to be done in two steps. With the first needle, finish the heel on the first sock, and pick up the sts on the first side of the heel. Then turn the heel on the second sock, and with that same needle pick up the heel on the first side of the second sock. Then with the second needle, work across the instep of the second sock, then the first. Then back to the first needle, and pick up the second half of the gusset on the first sock, work across the rest of the sole. And lastly, with that same needle, pick up the second half of the gusset on the second sock, and work across the rest of the sock.
It seems odd at first, but if you think through it, it's actually pretty logical. It's exactly how you do it for a single sock: first side of gusset pickup, work across instep sts, then second side of gusset sts. It's all about keeping the sole stitches grouped together on one needle, and the instep sts grouped together on the other.
And then once that's done, it's easy!