METHOD 1:

generate the ddl for all the tables that have the lob (use indexfile option during import
or use dbms_metadata).
Please have a look here for examples for both methods.

http://www.orafaq.com/forum/t/22316/0/
http://www.orafaq.com/forum/t/20862/0/

edit the ddl and replace the tablespace PROD to USER/TEST.
Make user replace all entries (both for table data segment and lob segment).
create ONLY those tables with LOBs in the USER schema
DO the import with ignore=y

METHOD 2:

Let the user have privs on the PROD schema (temporarily, give quota on the the prod tablespace) 
do the import as usual.
all the regular tables  will be created in USER tablespace.
ONly tables with LOBS will be created in PROD tablespace.
Now MOVE those tables along with lobs (owned by TEST USER by residing in PROD tablespace) to TEST tablespace.
Only everything is all set, check whehter all tables and lobs are in TEST tablepace.
IF so, revoke the  RESOURCE role
grant quota unlimited ONLY ON test tablespace.

THere is something you need to know.
THERE IS a known intermittent bug you may encounter in oracle 9.2.0.1 if you follow the above procedure.
Moving the lobs may create some ora-600 internal erros or soft corruptions may occur.

Please have look here for example to move a table with lob segment.
Make sure you move the table,lobsegment and lobindex.

http://www.orafaq.net/msgboard/server/messages/20908.htm