Very interesting conspiracy. But frankly, I don't think Roberts needed to be pressured to bless Obamacare. Roberts is from the establishment. He is a pragmatist. He is not especially "conservative" whatever the hell that means, nowadays. He avoids the "activist" label and he has consistently sided with the State and refused to make rulings that undermine the establishment.
Hedgepeth v. Washington Metropolitan Area Transit Authority, 386 F.3d 1148
Hamdan v. Rumsfeld
In other words, he is a statist and serves the State at the pleasure of the State.
His Obamacare ruling was no surprise considering his philosophy.