PostgreSQL - partial dump of large objects (pg_largeobject table)
I managed to resolve this issue as follow (2nd considered solution - revisited):

All in a while cicle, for every file:


select file_id , file_version, oid and put them in 3 variables
perform a [lo_export] of pg_largeobjects that require oid a path+filename to be defined. The filename will be the concatenation of the file_id and file_version. 
during lo_import new OID will be generated. But using the filename defined above, I can perform the last stem: 
update all the rows in the files table in order to make them point to the new imported pg_largeobject records and mantain the relation consistecy