Replying to my own post...
Nope - that didn't work. I'm still getting the 'headers already sent' thingie. The weird thing is it used to work fine - but I'm experiencing some vB3 weirdness. Inline attachments and thumbnails quit working about the same time. I've been working with vB on this. For now, running the thing as a vB3 cron job appears to be working but wouldn't be my first choice