[Koha] adding existing items to acquisitions

Hi, how can I add existing items to existing acquisitions? The normal procedure would be to first "order" an item within an acquisition's basket, and then have it "received". But I am trying to reconstruct past acquisitions (for the sake of my library's records), that had been dealt with outside Koha. Existing items are already populated with costs and source of acquisition. (I wouldn't mind acting directly on the database by means of mysql commands.) (Batch procedures would be helpful, as I have plenty of items to be added to acquisitions, and I can easily select their itemnumber into groups by means of appropriate mysql clauses.) Many thanks. Giuseppe.