That's the nature of the changeling tho - that choice, that razor's edge between humanity and fae. Its the overall theme of the Dresdenverse: "There's No Free Lunch."
I'm uncomfortable with the greater glamours (as per the book, its for pure fae), I'd still let it in, but boy, that certainly foreshadows to me what your final decision will ultimately be.
And why would a GM need to railroad it constantly? If it was me, I'd wait till it really, Really, REALLY hurts to make that choice.
Its the climax of the story. Chips are all on the table. The fight's going down the toilet sideways and everything is not looking good for the good guys. But oh, hi there Dad. Fancy you popping up. What? One more boost to the old toolbox so *I* can save everyone I love and.. what? The world?
Hmmmm.
HMMMM.
HMMMMMMMMMMM.....