I wish I'd gotten that out earlier. But to be completely honest, I just had no idea how to do it. I searched Google and found nothing. I posted on several tech support forums and got no answers.
Then I stumbled across a setting in PowerPress that lets me keep the primary feed restricted (since many aggregators won't accept a file larger than 512kb) while having a different limit on individual categories. Since podcasts are already their own category, I gave it a 999 limit, left the main feed at 50 posts, and everything works as expected!
Holy or unholy. Only one homie. Only this gun. Lonely 'cause don't anyone know me.