You don't have to reach the bridge, you just have to run away from the machine twice.

I normally beat it with Thundara, Water, Quezacotl and Double. Elem-Atk helps, as does Str-J and Mag-J. Limit Breaks are good.
Generally, I give Squall 100 Thundara spells and junction them to his Elem-Atk slot. I boost his strength and HP, too, then lower his HP till it's critical. This allows him to do continuous, powerful Limit Breaks. Makes fast work of the Black Widow.