We are planning to move our application on a centralized system, which can be used by people worldwide. The need is to track and use time zones for each customer.
The application was not originally built with this requirement in mind and uses a few 1000s of sysdates internally. Also "DATE" is used commonly as the datatype. Ideally what we are looking for is a possibility for overriding the "sysdate" function. Is this possible?

Any other suggestions will also be appreciated.

Thanks in advance.

DB details

Oracle v 10g (10.2.0.3.0)
Application is java based.