There are a few "built-in" parameters that let you pick up the executing user's ID / LANGUAGE / etc
From the studio manual;
Built-in parameters, which automatically take their values at run-time based on the current user settings or system context. Built-in parameters are specified using the following syntax:
@SELECT:PARAM:PARAM_IDENTIFIER[:ALIAS]@
or,
@WHERE:PARAM:PARAM_IDENTIFIER@
Where:
PARAM_IDENTIFIER is one of the following:
USER_ID
USER_NAME
LANGUAGE
LOCALE
So you want
@WHERE:PARAM:USER_ID@