Cubes are a totally different beast in this context.
The short answer is, that you can't in a calculated field....
However, if you know a little MDX (the query language of cubes) you can create your own calculated members. The syntax of the calculated member will be something like ([Dimension Name].[Attribute Name].[Member Name], [Measures],[Measure Name]) or as an real example: ([Customer].[Customer Name].[Inspari], [Measures],[Sales])
This will give you the value of Sales for the customer named Inspari
Hope it help