I never try to defeat the Midgar Zolom that early (then again, I also power-level so that I'm at least LV 20+ by the time I leave Midgar), and don't bother coming back to whomp on the Midgar Zoloms until right AFTER the Gold Saucer, and then I just have one charachter with one of my Enemey Skill materias and the fire ring (null fire), and another charachter with the other Enemy Skill materia and elemental-fire on the defense (if I'd been REALLY twinking the game, the elemental-fire would have been to the point where it would nullify elemental damage), and I'd use Laser until the Midgar Zolom's HP < 500, at which point it would use Beta, and then once I learned that enemey skill, I'd kindly finish off the poor creature with its own attack

Of course, I'd also take a detour from North Corel to go down to the chocobo tracks and wander around (with the chocobo lure materia equipped) until I got a chocobo to appear with a chimera, then I'd just harass the chimera until it used aqualung, on my party. Needless to say, with Barret equiped with my best enemy skill materia (matra magic, flamethrower, laser, aqualung) I was able to defeat Dyne in all of three rounds.