We might be nagging at the same thing here. It's not the unused holes as such, but what pattern, or spoke sequence he'll end up with. For a 24H rim it'd be obvious, DS-NDS-DS-DS-NDS-DS ASO, all nice and symmetric. But now? empty-DS-NDS-DS-empty-DS-NDS-DS-empty .. Might not be too bad after all.
Assuming the rim isn't drilled for definite left flange/right flange spoke orientation it might work out OK.