Create a parameter for user and date and make user as optional parameter. If you need a particular user for all date range you can filter by using user parameter. And for improvement purpose you can take the report according to alphabetical order. This might require multiple scheduling of the report but still you will get an output. If it has to be run reccuring create a report and create run schedule with user parameter.
User parameter will be like User Like 'A', User like 'B'. etc