Distinct Filter In SQL Reporting Services

Hello All,

I've got a stored proc that I can't change that creates a quite large
dataset and takes in 5 parameters. I need to be able to have each of
the parameters selectable from a drop down box so that as you go
through the list of parameters you restrict the results. I have it
able to load the parameters but I end up with this:

Location-
LONDON
LONDON
LONDON
NEW YORK
NEW YORK
NEW YORK
NEW YORK
TORONTO
TORONTO
....

Any idea how i can filter the list of locations by distinct? from
within SQL Reporting Services. I tried a temp tbl in query analyser
and that works but SQL reporting services doesn't like it.