Custom Report - Limit number of selection to activate Defer Layout button

We use the custom report on a very big dataset (50 M rows) and we use currently the Defer Layout button.
But it can take a while to calculate and generate and the users get a time out.

We would like to add a parameter with a max number of dimensions/measures that the user could select. Over this max, the user would have a message askin to select less information.