Case sensitive Oracle 11g
Yep, it's really strange why SEC_CASE_SENSITIVE_LOGON should not be used for this if it's especially designed for the purpose.
I can suggest in this case maybe just use some external authorization method like Oracle Identity Management, e.g.. It's much more complex and require additional infrastructure installed/configured and maintained, but users' credentials will be stored and controlled (including case-sensitive passwords) outside of the database and becomes independent on the database parameter value.