It may well be Bob Jackson could work you in, as rebrazing a rack mount is quick work. If you were near me, I'd do it for you right away.
Lacking that, the Tubus seatstay mounts aren't a bad option -- just make sure they're large enough to fit your stays. If you have a Nomad (I don't recall...), then they need to be able to wrap around 19mm.
The reason they work okay is the bottom mounts bear the bulk of the weight, while the upper ones tend to serve as fore-aft locators. Where you're in a hurry, these should get you going...but a proper repair would be most desirable.
Based on repairs I've done, the biggest component in upper mount failures seems to be loose rack bolts, allowing the rack to fret on the upper mounts, leading to failure. Looking at yours, however, it appears there wasn't full penetration of brass into the joint ("cold joint") -- but that is just going off of one rather dark photo. I'd have to see it in person to say for sure.
The silver lining to this is you found it while prepping the bike, instead of mid-tour. You've got more ready options as a result.
Please let us know how you fare.
All the best,
Dan.