I'm facing the same issue, I tried different options without success:
Command=ME23N DYNP_OKCODE=MECHOB;MEPO_SELECT-EBELN="0051013185";
or
Command=ME23N DYNP_OKCODE=MECHOB;MEPO_SELECT-EBELN=0051016379;DYNP_OKCODE=MEOK;
...
The only thing I achieve is showing the popup to select the PO with the incorrect PO number, but that's only what I get...
Did you solve the problem?