Using Dynamic Formula Parameters in Report Manager Subscriptions

I have a situation where a user wants to subscribe to a report that takes a date range, with a start and an end date. They want to be able to have the report be able to run against a specific time frame for every subscription. So for example, the report would run every Monday, and show the data from the previous week. Another user would want the same report to run every Month, and show the previous Month. so if i have a paramater of Start Date and End Date, how could they put in a value to indicate this constantly moving date range.

Something like Start Date = Beginning of previous Month and End Date = End of previous Month, and every time the subscription fires, it recalculates the dates.

Any guidance appreciated.