A little update;
I called 1178 this morning, and they were a little cagey. I told them I entered 60 days VE, and got a 30 day extension at immigration. I said "Can I get a 60 day extension to visit Thai wife?" and the guy on the phone indicated that it was possible - but wouldn't confirm it. He said "Because you've already had an extension for 30 days, I don't know if you can get another 60 - you will need to confirm with your local office."
I'm still going to try the other office to see if they'll do it, but I'm not so sure it's doable now.
Question; If I don't have enough space in my passport for the full page Lao sticker, do you see any issues with me walking in and out at Chong Mek? I'm thinking if they stamp me out, but I can't get a Lao stamp, will they allow me back in rather than leaving me in no-mans land between Thailand & Laos?