When you're doing socks with one inside the other you can actually do any pattern you want that can be worked in the round.
What's happening is that the right side of the inside sock is facing you, just as the right side of the outside sock is. You just happen to have the stitches from the inside one alternating on the same needle with the stitches from the outside one and you're knitting each alternate stitch with it's own ball of yarn. So whatever pattern you're doing on the top one will also be done on the inside one.
Sorry, that sounds a lot more complex than it actually is. Once you just go for it and do it, no matter how dizzy you might get at first, suddenly the penny will drop in the slot and you'll go "BINGO! I've got it!".
A couple of things I'd like to recommend to start with. First, it's helpful for your first project to use different colored yarns for the inside and outside pieces. Yes, that'll mean you'll be making two sets of whatever you decide to make, but it'll be a lot easier to do in the beginning. As you become more comfortable with the technique you can move on to using the same yarn for both pieces.
Second, select a pattern that has no complexities like turning heels. The Knitty article gives great directions for this but for my first inside-out project I made leg warmers, one in creme and one in blue and then later made another set just like them!
They really came in handy for Christmas presents last year and I loved doing them. (I wrote the pattern for them so if anyone wants it let me know and I'll be glad to send it to you!)
As soon as I have the leisure to try out doing the socks this way, complete with turned heel and using the same yarn, I'll be getting back on the double-knitting-inside-out bandwagon for sure!
Just keep checking your project as you go to make sure you haven't accidentally knit any stitches together (just a little tugging the layers apart as you turn your work will tell you if you have) and pay attention to the finished size of your pieces. The inner leg warmers came out smaller than the outer ones for me. I suspect that's just the way I was knitting but it might be something you want to be alert for.
Let us know how it goes for you. It's an exciting technique that I'm hoping you'll really like!
Happy knitting, (times 2)