You'd have to sample carefully, but since we are limiting the discussion to non-destructive techniques, I think EMP or XRF (X-ray flourescence) are the only options. Both of those techniques can be aimed, so you could (with EMP, at least) get measurements of the different layers in the pamor. I'm not sure how small an area XRF samples, but they use it on artifacts in museums, so it's very non-destructive. The trace elements are uniformly distributed through the metals, so you'd only have to take into account the mix of the two metals in the folding process, and sample accordingly...
...or so I think!
INAA (or EMP or XRF) would be good if you could take some filings off the end of a tang, but then you couldn't be sure the tang was the same metal as the pamor, and you'd have potential issues.