Not without using the Mazo, but rather not having it inside of them. Like I said, provide any manga/databook evidence that proves Hagoromo not having it inside of him when he was a Juubi Jin, please. It's a rhetorical request, though, I know there is none.
We don't know that for a fact. What we know, though, is that every single Juubi Jin we've seen so far had the bijuu sealed into the Mazo beforehand.
To be honest, I don't see how this is relevant. I'm well aware of the fact that we can go into pseudo sophistic discussion on what is what in a shonen manga and what the author meant here and there, and I don't feel like doing so.
Because the Mazo is the vessel for them, why does he need to mention it? In nutshell, yes, Juubi is the fusion of the bijuu. Just like the fusion of floor, eggs and milk can become a pancake. But in order for them to fuse into the Juubi, you need them to be sealed into the statue first, otherwise the whole sealing issue would've been pointless, much like you need to bake the fused mass of the ingredients I mentioned in order for them become a pancake. I hope you get the analogy now, it's not that complicated and to be honest, I think you're arguing just for the purpose of arguing right now.
Naruto has the chakra of all the bijuu inside of him right now. Why doesn't he become a Juubi Jin? Exactly how do you estimate the amount of chakra needed for that? Why did both Obito, and especially Madara (considering that the Juubi has just been dismembered again, and the beasts obviously don't need, as you called it, 'rejuvenation'), have to re-seal all the tailed beasts back into the statue when they intended to become Juubi Jins? Obito had a very small portion of Hachibi's chakra, and even a smaller one of Kyuubi's. On top of that, why didn't Obito just seal all the bijuu inside of him as Akatsuki collected them? Why wait and bother with the Mazo?
The answer is the following: Yes, the Mazo is a crucial part of the Juubi. You can deny it all you want, I don't really care, because my initial intention of entering these debates was to possibly reconsider something about the manga I've known so far given that I'd receive some valid arguments/manga evidence, but, as expected, I've received nothing but a waste of time.
I don't think it can, for I've just pointed out a dozen of holes in your explanation. Sorry, but I don't accept it.
Just like Naruto contains portions of all the Bijuu now, so he has all the necessary ingredients... oops?
And we should think that there is a borderline amount of the chakra you need to gather in order to become a Juubi Jin rather than just sealing it all into the Mazo which turns into Juubi after that, much like we've seen in the manga a few times, because... why, exactly?