It is possible to use Parameters to define the fields you would like to filter by and then use these parameters in Calculations to achieve the OR functionality.
I have attached a workbook that shows this example using the Order Date and Ship Date on the Superstore Sales example. Can you have a play about with the parameter sliders and let me know if this is what you were looking for please?
Thanks for your reply. I did use calculated measure to solve this, however I think the problem was in date conversion .. got error "command text was not set for command object". Source database is Teradata.
[Date1] <= DATE ("04/15/2012") or [Date2] <= DATE ("04/15/2012")
I finally avoided this by defining a date parameter and then using that in the calculated measure.