Financial Reporting Studio - If/then statement

For the Financial Reporting Studio experts out there:

Trying to write a if/then formula in FRS.  basically saying: if last year value is zero (column D), then return "n/a" because the % increase is irrelevant.  FRS will not recognize a "character value" as part of the false or true condition - like excel allows so nicely in it's own IF statements.

IfThen([D]=0,"n/a",Eval([B]/[D]-1))

I even tried typing in "n/a" as text in another hidden column, then referencing that character below for the true condition, but it will not allow me to insert another formula (ex GetCell) as part of the true or false condition.