Reporting Services, access dataset from RDL custom code module

Using Reporting Services in SQL Server 2005, is it possible to access the report's dataset(s) from within a function implemented in the report's custom code module?

The custom code module I'm talking about is the one you see when you select Report - Report Properties from the VS 2005 Report Designer, in the Code tab.  I'd like to be able to perform lookups into the report's datasets within the body of a function in this code module.

For example:

   function LookupStoreName(ZipCode as string) as String
      '// ... code to access dataset, do some logic, return a value
   end function

To save you some trouble: yes I know that I could call a SQL Server function in a dataset definition. I need this functionality to be callable from a textbox value expression and not as a Fields!XXX.value or Parameters!XXX.value reference.  It needs to function independent of the report's main dataset.

-- CraigStart Free Trial