hide dimension member from dashboard query browser / query prompt selector

Hi:

  I am using Dashboards and IDT (4.1 SP5) with a universe based on an OLAP data source. I have a hierarchical dimension for Date and I want to hide the lowest level (day) from being available in the query prompt selector.  I have tried in my universe (unx) setting the day member to hidden but it still seems to be available to the user when the user is prompted to select values from the date hierarchy.

Does anyone have any ideas?

Thanks,

Alasdair