Change value of SSRS report parameter based on the input of another parameter

I have a SSRS 2005 report with three parameters: @FromDate, @ToDate and @Period. @FromDate and @ToDate default to the first day and the last day of last month, respectively.

The @Period parameter is a multi-value parameter. So if I choose for instance "Current quarter", I want the @FromDate and @ToDate to change to the corresponding values based on the input in @Period.

My problem is not getting the correct datetime expressions, but rather how to make the parameters interact with each other as desired.