Manga/Anime I read/have read/tried to read:
What chakra type are you?
From ancient times, there existed people, who were searching and thriving for a way to surpass their human limitations, to obtain methods and skills that would allow them to reach highs that no human could ever come close to... then, the answer came at the end of XX century, with it's technology that finally granted their cherished wish... at that time and even to this day, not many knew the purpose, the true meaning of what was created and shared with the whole world... the only thing that is widely know, or perhaps a realization that humanity finally reached, is a proper name for those people... in this day and age, we call them: "Spammers".
Anyway, I think it would be possible to enter a full bijuu mode without being all buddy-buddy, or being taken over by the beast, by forming some kind of contract/deal. For example, offering 1000 lives (to Shukaku) for it, or releasing the bijuu (without a fight) after 10 fully controlled transformations.