How to cancel a line of a multi-line invoice after it has been sent to GL?

Hi there,

We have an invoice with many lines, created last year.  One of lines was applied to a wrong PO.  How can we reverse this line (leave the other lines alone) and move it to the correct PO?

My thinking is to create an one-line invoice with negative amount and apply it to first PO.  Then create second one-line invoice and apply it to the correct PO.

Question: if this will work and if there is a better solution?

Thanks,

Ning