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Let a row or column clean up a box.
Box/line reduction flips the direction of a pointing pair. If a candidate in a row or column only appears within the cells that fall inside one particular box, you can eliminate that candidate from the rest of that box.
This works because the digit still needs a home somewhere in the row or column, and every legal option happens to sit inside the same box, so nowhere else in that box can hold it.
The live grid below highlights a row alongside the single box it constrains. Watch the candidate panel update as you hover different cells.