Yeah, check out my z-curve-sweeper or this:
That same technique is used in the z-curve-sweeper if you don’t wanna do gumroad… It’s using face-corner index-magic, as you’ve guessed. The z-curve-sweeper stores the result in uv_map face-corner named property so it’s easier to work with - it’s easy to port the above file to do something similar (Thanks to user @quellenform for their help).
@Debuk : not quite - that just happened when using points to transfer the UVs instead of Face-Corners… because the U/V value is going from e.g. 0.9 to 0 on the last vertices, instead of from 0.9 to 1 (since the final and fist vertices are the same) - using Face corners fixes the issue and you don’t get that band. Check out Higgsas’ and my node-groups for solutions that fix it.