I'm not sure about keeping the stops behind the center - not sure there's room behind the drawers.

Bumpin' back up to get others opinions...

For more info & detail here's my best attempt at a dwv diagram for my situation... The blue box is the room I'm working on. Solid lines are things I can visually see - either the wall is out or the floor is up. Dotted lines are my best guesses at where things are. The red room is an adjacent bathroom.

After seeing you pic, I think I'll back away (just a little ) about the concerns about drilling the studs. It appears that you would only have to drill one more stud to do the drain. I think I would notch that one. That would leave you 1 1/2 material on the far side. Put a piece of strap iron on the front edge, you need nail plate anyway. A strap about 1' long with at least two screws top and bottom should restore structural integrity of the stud. I also notch studs for supply keeping them at the front edge and on the interior side of the insulation. Hopefully the right hand sink won't be too far away from the vent.

Thanks Harold - I'll take that approach I think. 2 questions...

1) Where does one get the strap iron things? I saw some of these type things @ Lowe's, but they were stainless steel and to me didn't look very strong.

2) How do I route the supplies around the existing drain? In other words, as you look at the picture, the supplies will have to be routed to the right, around the drain somehow. But the drain line takes up the whole wall cavity.

Strap iron is just flat metal at HD or Lowe's where they have short lengths of flat metal, angle iron and metal rods. Get the thinnest you can. Something about 1/16 would be best (I don't know what gauge that is). Any metal shop would have thinner stuff, its going to cause bow in drywall but it will be hidden by vanity. 1 to 1 1/2 wide should do.

Hard to tell from photo if you have any space between drain and exterior wall surface. If you do, cut drain right above plate, install a 22 1/2 turn, pushed against exterior wall, then short piece of pipe. Then another 22 1/2 back to drain. If you can't find 22 1/2 use 45's. Hopefully that gives you 1/2" between drain pipe and drywall. If you can't do that, just put supplies on front edge of stud, drywall above and below, cover with tape and mud. Be hidden by vanity.

PS
After thinking about it for a minute probably easiest to just put supplies on front edge of studs. Just tape and mud over to keep drafts out.