How to create measure filter on a dimension not shown in report

In the Adventure Works cube, how do I write the MDX to answer this request:

"Find count of customers having order with more than 3 quantity"

The MDX below doesn't work.  It still returns all customers.

select 
	[Measures].[Customer Count] on 0	
from [Adventure Works]
where filter([Internet Sales Order Details].[Sales Order Number], [Measures].[Internet Order Quantity] > 3)