Interesting theory. I was assuming Bird Cage was some sort of power from Doflamingo but that theory of yours somehow "tingles" my senses.
We still don't really know the exact scale of Doflamingo's fruit abilities. More than once has Oda made it so that despite a fruit having a main ability, from it, other seemingly unrelated ones exist. For example, Bartolomew's paw paw fruit. It has the ability to deliver powerful pushes...but it goes way beyond it in a direction most wouldn't relate. Perhaps Mingo's fruit has some sort of these "less direct" abilities, one of which is to completely control someone else. I say this because we've seen he can physical control someone else like a puppet with his strings but that doesn't exactly mean he can make them use their powers or that he can control their mind.
I also have a doubt about something...isn't one of his main lackeys missing? I get a feeling someone is missing from this whole thing.
