And this is again the part where a normal human being would narrow his eyes and go 'how am I supposed to trust your word.' The Winter Soldier does the first and skips the second and then dismisses the concern. Any option aside from cooperation, which means Steve not using this opportunity to escape, involves a bodycount, and he's gotten enough of Captain America's measure to know the lengths he'll go to in order to avoid that.

He moves into position beneath the fire escape but doesn't ready himself at all, no helpful stirrup or bent knees for Steve to use as a platform. The fingers of his left arm flex once though, the serpentine rippling of the metal plates visible briefly under his sleeve.