using system dates to restrict BW queries

Hi, I'm just migrating from XIr2 to 3.1 and we are now able to put conditions in our BW universes.

In a simple test I am able to create a condition as follows that returns just my 2008 data.

<FILTER KEY="[0FISCYEAR].[LEVEL01].[NAME]">
    <CONDITION OPERATORCONDITION="Equal">
        <CONSTANT CAPTION="Z12008"></CONSTANT>
    </CONDITION>
</FILTER>

What I would like to do is something like CAPTION="Z1"+ TO_CHAR(SYSDATE, 'YYYY') so that I can use the filter to get the Current/Last year/month/week/period etc.....

Any pointers???

Thanks

Nick