You could split the amount of your 2 tax codes in PO item tab and GL Account type
For example you have 1 PO item with amount 5000 and need to separate into 2 tax codes:
In the PO item, in MIRO, changed the expected amount i.e 3000 and inserted the 1st tax code (no changes was made to qty).
In the G/L account tab of MIRO input the rest of amount i.e 2000 with 2nd tax code:
The invoice was posted with the correct vat amount with 2 vat codes for the single PO item.