Simple Formulas in Webi in Design Studio, i.e. replace # with other text

We have a few formulas in webi that are useful for manipulating text and need the same in Design Studio

For example, when reporting on Sales Rep and there are Not Assigned #, the requirement is to replace the # with 00000.  The users think the # is bad data. Now, I know we can replace the # in BW, but it is global and we only want to replace the # for certain infoobjects.

In webi, we can do this simply as a formula

=If([Sales Representative].[Sales Representative - Key]<>"#") Then [Sales Representative].[Sales Representative - Key] Else "00000"

How can this be done in design studio?

Any help is appreciated!

Lee Lewis