Current client had a DBA that did the same thing ... built a new dataserver from scratch, enabled RDDB for a handful of user-created temporary databases, didn't notice the warning about a 30-day graced license, left the company, and when the 30-day graced license expired ... wellll ... let's just say anything touching those temp db's didn't work.
Some cursory searching of the manuals, solved cases (@ sybase.com), and the SAP KB didn't accomplish much. While dropping/recreating the temporary databases should work, I just updated one of the status columns in sysdatabases and bounced the dataserver.
Which status column did I update? *shrug* I don't recall jotting down the details as it was fairly simple to see the difference in status values between tempdb and the user-created temporary databases. [NOTE: The ASE SP100 Reference:Tables manual doesn't list bit settings for RDDB related attributes.]
If you decide to go the 'update sysdatabases' route and you're not sure what to change, post back here with the sysdatabases records for tempdb and all user-created temporary databases.