Hi,
There is either a misunderstanding or some semantic issue here: 'reserved' budget or 'committed' budget equally means budget consumption, if the transaction is not 'statistical'. If there is no data, at the time of PR, which would allow to determine budgetary line (address) for consumption, then no 'reservation' can be made. If the data is, however, sufficient, then there is no need in creating EMF, as PR itself will create commitment, which would be further consumed by PO.
Hence, I agree with previous responses: your business requirement is not clear. Maybe, you can elaborate a bit...
Regards,
Eli