If I understood, you need to select dynamically the dimmention of a graph, with (for example) fiscal_date or calendar_date.
You could try creating a INLINE table, with only two registers in a field (this field must be different than other in the application)
LOAD * INLINE [
The 'date_type' field is what you will select, with a simple list box. The content of 'date_type_field' is the different field names that contains one or other kind of date.
Now, in your graphs, add a 'Calculated Dimention'= date_type_field
Your graph will get the dimmention you have selected in 'date_type'. You should check 'Always one selected value' in the listbox of date_type, because if you don't do that, the graph can't know which one to use.