Selecting Key Figures in any format before executing a query result

Has anyone seen a solution whereby a user can CHOOSE the Key Figures they want to be displayed in a query result at run-time before the query is executed?

I know it is possible to filter on a set of Key Figures in BEx but I'm looking for the small possibility that someone has found a way to do this before the query is executed and not after...

(I'm guessing it's not possible from my experience but you never know!)

thanks in advance,

Peter