Hi,
I am not sure- why your business going to release 1000 Purchase orders at a time!
Why not advice to your business to release Purchase order as and when requires day by day based on release code assigned to releaser.
If requires design a custom transaction code( ZRELEASE) and pass to release all Purchase orders for a single release code.Cross check Function Modules for custom transaction code( ZRELEASE) design.
1. BAPI_PO_RELEASE
2. ME_RELEASE_PURCHASE_DOCUMENT
3. WOD1_RELEASE_PURCHASE_ORDER
Regards,
Biju K