Yeah, but in this case is the universe just the dots on the surface of the balloon or is it the whole balloon with its entire volume? Intuitively I think it's the latter (although there's probably no "hard" edge that's bounding the ends of the universe like the rubber of the balloon), and if that's true, you could measure the speed of one wall getting away from the centre or the speed of two opposite walls getting away from each other.

I could be wrong of course, I'd be happy if someone points out what I might be missing.