Discovered how to set a server filter but the problem is that the dashboard took ages to load. it's painfully slow.
I encountered a similar situation few months ago.
Here's what I did: I appended a single Row in the dataset which is accessible to all users.
This record contains all the Measures as 0 (Zero) and all the Filter fields as (*Select ...)
Publish the dashboard with the this Dummy Record in the Selection Filter
So when any user logs in, the dashboard is always empty and loads quickly.
The dashboard will only populate when the user makes a selection from the drop down menu.
Let me know if you want a mockup of this idea.
I will try.