it is not possible in the report itself - the report just uses whatever you have in the qvw - but of course you can use functions like AutoNumber() and maybe a mapping_table to encrypt or otherwise scramble text and numbers, depending on the username (OSUSER())
P.S.: The possibility posted by Luis is also great - I wasn't thinking of that. However, I guess that only works on an on/off basis, not dynamically? - so it would somewhat force you to duplicate your qvw - one "cleartext" one and a scrambled one.