Just a though but it seems to me easier to create a single sidebar for all of your clients and have the Widgets sort out what information to display. Your ‘Reports’ widget can check for the logged in user and determine what information to show, for example. Maybe that isn’t quite the logic you want but I hope it gets the idea you across.
You could put a function in your functions.php file that would get all of your client/users and loop through creating sidebars but that strikes me as very, very inefficient and I’d expect a noticeable performance hit with more than a few clients. Plus you’d still need to go through and populate all those sidebars with widgets. It could be very time consuming.