Is it somehow possible to tell Hibernate to override the primary key generated by a sequence on some condition?

For example i have an entity with this primary key - int:

@GeneratedValue(strategy = GenerationType.SEQUENCE,generator="pk_seq")
private Integer id;

normally im perfectly happy with this, so I can create objects and call:

session.save(Object);

and hibernate creates the primary key.
but now i want to program a tool to import database entrys from csv-files, where the primary key that should be used is already specified:

id;day;month;year;time;historical;quality;att1;v1;att2;v2
1;12;09;2009;16:04:48;;;1;+26.3;2;34.27

so i create my objects:

Object o = new Object();
o.setId(1);
...
but when i call
session.save(o);
hibernate uses the generated key instead of the one assigned.
can i tell hibernate to generate a primary key only if none is assigned?