as far as I know, you can't...CR sets up the parameters to the stored proc.
since I hate CR parameters...especially the datetime, I would use the calendar and then in the stored proc strip off the time component.
luckily I don't have to use the CR parameters (we have designed wizards that allow us to completely control the user input for parameters, then we pass them to the stored proc, and finally pass the results of the stored proc to the report...which also allows us to postprocess the data if we want/need)
HTH