Other than setting up different movement keys for your clone (just disable the arrow keys on your main and use these on your clone for movement could be an easy way) I don't know of another option to move your clone.

Even if you have separate movement for main and clone (could be a finger twisting hazard) the time lost with targeting and positioning the pair every single time would take a lot of the fun out instead of having fun. Macros for moving (other than a spread out or follow macro) esp for melee classes (which isn't the easiest route, and even harder in pvp) are generally a bad idea.

So I'd suggest to go with Voodoogriff's advice, let your main tag the mob and run through him (then turn and face the mob) so that you your clone is automatically aligned and set up for the backstabbing (I can see how it could be advantageous always having one striking from behind).

Something you might want to consider (when it comes to attacking) is the timing of certain abilities, for example you don't want both of your rogues to kick the same spell at the same time,
/castsequence kick, <- on main
/castsequence ,kick <- on clone
binded on the same button would be the simplest way to prevent blowing the cooldown on both characters, and you can do this for others as well (save the kidneyshot on your clone for when your main's KS wears out, not during the same time, don't blind the same guy at the same time, etc..).

It's just a matter of setting them both up so they're tuned to one another. Probably will take a short while though