EDIT - Added a "for" in panel one ("a few times FOR testing")
For the record, I did not work backwards from that last option! I was legitimately brainstorming ways to make the spell less costly to cast before getting "trades" involved!
Creating a smaller duplicate? Makes sense!
Creating a duplicate that doesn't do much of anything without manual control? Makes sense!
Duplicating only the bare minimum necessary? Makes sense!
So yes, I genuinely don't think it's a stretch that it's an option. It makes sense (in so far as any magic makes sense, at least). That doesn't mean there's any chance that Nanase's actually going to do that in the comic, but still!