You should never bump start a car with a cat anyway.
Not that it helps with the original poster's problem, but I've always wondered about that piece of advice which I've read in lots of places - you are in good company to point that out, but I don't understand why that's the case.
If you had the car rolling at about 20km/hr and engaged fourth gear, gently engaging the clutch, it really should turn over quite smoothly, possibly more smoothly than it would be turning over with the starter motor. The faster you can get it going, the smoother it will be. I don't see how this will cause lots of unburned fuel to enter the exhaust (no more than during usual starting). What's the difference between turning it over on the starter motor and turning it over by roll starting? And why should it backfire into the inlet manifold? Shouldn't it start easier with more voltage available to the ignition and injection systems?
Incidentally, hybrid cars turn the engine over with the traction motor at about idle speed to start it. You'd think they'd be having these backfiring problems or unburned-fuel-in-the-cat problems.
I roll-start lots of cars, particularly those where the alternator has died and I want to get it home without unduly flattening the battery.
On the other hand I have seen people trying to push-start cars in 1st gear and that is horribly rough. Perhaps this is where it gets the bad reputation, and the fact that aside's engine now seems to be damaged