This would need to be a feature of your pivot table tool. AS will not allow you to force a user to always have a particular dimension filtered unless you restrict a user or role to a particular member (clearly not what you want).
Excel does not do this. With some VBA, you could create a workbook with the pivot table pre-defined that would prompt the user for an account number when it opens, but they would still be able to remove the dimension from the page section later. I am not sure if you could really prevent that.