how to sort via multi value parameter in ssrs

I have a parameter with multi values. when the user selects ,he get of options like acount name, first name, last name.

so if user selects firstname , the data has to sort by firstname.

if he selects acount name , the data has to sort by account name.

please help me how to sort the data using parameter with multivalue? in ssrs 2008.

Thank you?