Make a prompt conditional based on the number of column values

 I would like a prompt to appear for users that have more than 1 value in a column but not for those that have only one value.  This would prevent the prompt from appearing for users that only have 1 value to select.  The reason this is needed is for our internal users.  They have access to multiple customer data where our customers only have access to their own data.  When an internal user opens a report all data opens and the report takes awhile to open.  After it opens they filter on the customer they want to look at.  I would like to add a prompt to the report for these users to choose a customer before the data loads but not want it to have to appear to our customers.