Are you working in stockinette? If so I think I would figure out how many stitches I need to decrease and would work decreases in the purl sts of the rib in the first round, assuming you are ribbing the top of the sock. If it's more than I wanted to do in one round, I would work about half the decreases in a round of stockinette and then the rest in the purls of the first round of ribbing. I'd try to distribute the decreases evenly and if working two rows would probably stagger them.
There might be something you'd find useful here, it's where I learned to knit socks. http://www.k1p1design1.com/socks.html
Good luck and I look forward to knowing how they work out for you and how you solve the problem.
What pattern are you using?
What does ML mean? I'm thinking I might be missing something important.