Dynamic paratmer values - Scheduling

[cielo]

I have a Report(created combination of 8 other Standalone reports using page reference), all reports has a common parameter(Month end date),I would like to schedule this report to specific email ids and it should run every month 15th and it should generate the report for last month end date. I have tried event Studio option though didn't find the exact solution. Also I would like to given an option to Users to run when they want(they can't execute report as it is taking time for parameters load).Is there a way I could create a job/event and that could prompt user to select a date value and run ? or can I dynamically parametrize...Please help with your suggestions.Ty