BI Publisher: Using XDO_USER_NAME in query for LOV

I have a report parameter, supervisor, based on a List of Values.  The query to populate the LOV includes a reference to xdo_user_name to get the person who is logged in.

However when I run the report I get this error :

"Parameter name: supervisor Missing IN or OUT parameter at index:: 1; Data source: hrDS; Query: select distinct PPF.FULL_NAME,PPF.PERSON_ID FROM PER ...."

When I hard code a user name such as 'JAMALM' instead of xdo_user_name,  the report runs fine.  Can I not use a system variable such as xdo_user_name in a query for LOV ?  If I can't then is there a workaround ?