Just demonstrating why it wasn't practical for him to apply in his home country, include information about his accommodations/purpose in the Philippines, and give them time to correspond with the US. The visa type was M and we had issued a chopped invitation letter, which they were fine with. It certainly wasn't the end of the world, and I wasn't seriously worried about him not being permitted to apply, but if he had bothered to reach out to them beforehand, we would have chosen a different path.

ETA: I forgot to mention that a potential downside to applying in an overly bureaucratic consulate/visa center is ending up with a crappy visa.