Don't know why I didn't think about This last night but could you weld the nut in? Just put a good tack on it?
Remove the head lights.. Get a 7/8 wrench(might have to bend the wrench a little) and hold the nut while you remove the cab bolt. But if you can weld it.. It makes it easier for the future.
If you will lift up on the cab enough to decompress the suspension some before you start to take the bolts loose it will help keep the nuts from spinning. As you loosen the bolts the weight will ease back onto the suspension so use some common sense as to how far you pick the cab up.
X2 on not using impact. I break the bolts loose with a ratchet and can normally turn them the rest of the way out with a 18V drill.