you can do it using formula. you have to create a pramater with values ascending and descending. then create a formula for e.g
let takes a paramter called "sortorder", so the values for this paramater would be "ascending" and "descending"
now create a forrmula "sort" which has following syntax
if {?sortorder} = "ascending" then
({table.field}; crascendingorder)
else
({table.field}; crdescendingorder)
promp the user to select sortorder.
In the record sort put this formula @sort. also place the @sort formula in pageheader and supress it.