I'll take a look in my copy, but there is really a very narrow range in which champagne yeast would be beneficial.
Most yeasts called "Champagne" yeasts have low nutrient needs and high alcohol tolerance. If you were fermenting the entire wort with Champagne yeast, from my experience, 1.062 to 1.028 is where I'd expect a typical wine yeast would end up.
Wort is made up of a lot of different kinds of sugars, some simple (like glucose), some complex (like maltotriose), some really complex (like dextrins). All yeast used to make booze can ferment simple sugars. Some yeast (and all beer yeast) can ferment complex sugars to varying degrees, but very few yeast (like Brett) can ferment really complex sugars.
So, if your stalled ferment was due to low nutrients or high alcohol, and if there were still plenty of simple sugars left over, then Champagne yeast might nudge the gravity down a bit. Wort is typically nutrient dense, and your beer doesn't have much alcohol, and probably doesn't have many simple sugars left, so I don't think Champagne yeast would help.
I think it's more likely the ferment stalled when the yeast ran out of simple sugars and are having trouble breaking down and eating the more complex sugars.
RE: starters with dry yeast, one of the really cool things the yeast labs can do is build huge energy reserves into the dry yeast. Within the first ~30min of being rehydrated they go nuts, but their activity tapers down to "normal" shortly after that burst. So that burst of energy isn't necessary, but it helps kick off a strong ferment. Once you've gone past that 30min window, the yeast will just act like normal yeast.