score:2
To answer my own question, the solution appears to be to get some locals to do the booking.
Reservations for Festzelt Tradition opened on April 1st at midnight. I put in my reservation for 8 people (smallest group) for 5 PM (earliest possible time) less than an hour later, with my non-German address & contact details. On April 15th, I got my reply: Diese Anfrage wurde vom Ratskeller oder vom Interessenten abgelehnt. ("Your reservation was rejected" β Germans really don't beat about the bush now do they...)
I then asked my buddy in Munich to try his luck in the same tent, same day, same time, same group size. Two weeks later, he got his answer: Gern bestΓ€tigen wir Ihren Reservierungswunsch. ("We are happy to confirm your reservation request.")
If you don't know anybody in Munich, there are various commercial services that resell seats under the guise of "tours", but they charge a pretty penny for the privilege: the going rate seems to be several hundred euros per person.
Upvote:3
Given you're still visiting on a normal weekday, it should not be an issue to get into some tent. But depending on the actual time you'll most likely be limited in your choice of tent.
For more details on tent selection and the full Oktoberfest experience, I can forward you to an older answer here on travel.SE