BOXI3.0: Metrics Universe
How can I define metrics in a universe based on a BW query/cube?
I have not tried this, however theoretically it should be possible by creating a predefined condition according to the documentation..
See the Customizing OLAP universes --> To create pre-defined conditions in an OLAP universe section in [http://help.sap.com/businessobject/product_guides/boexir3/en/xi3_sap_olap_universes_en.pdf], here you can use the @prompt function on the dates as per the metric definition requirement.
Hope this helps