As a counterpoint to daniel's answer - whom I'm sure, in all sincerity, makes perfect crème brûlées every time and I don't doubt that you can do the same by following his method - I have made a great many (albeit substantially less than five thousand) of them and have never heated anything except the water that goes into the bain-marie.
As long as you strain the mixture and use a bain-marie, and fill that up sufficiently with hot water, it won't curdle. At least not in my oven or in any of the ovens I've used in the past. That is in fact what a bain-marie is for. You might think that the radiant heat of the oven would overheat the custard anyway, but... it doesn't. Not as long as you use a relatively low oven setting and don't use the top rack.
As I said, I haven't made five thousand, but I've made several hundred and have never experienced curdling despite the lack of tempering.
If you want to prove it to yourself, then next time you make it, pour one serving into a ramekin before tempering the rest of the mixture. If they turn out the same, then you can skip that step entirely.