Hide parameters based on another parameter using dates

Referencing this topic: Relative Date and Custom Date filter

1) I want to take it a step further and hide the relative dates (Start and End date Parameters). 

OR

2) Can I populate the start and end date parameters based on my selection?

For example:

Past Month would display 6/1/18 in the start date and 6/30/18 in the end date.

YTD would display 1/1/18 in the start date and 7/12/18 in the end date, etc

If that is not possible then I just want to be able to hide the start and end date parameters unless I choose CUSTOM.

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Here is the case statement for the drop-down Date Filter:

CASE [Select Range]

WHEN "Most Recent Date" THEN

    //Sunday

    IIF (DATEPART('weekday',TODAY()) = 1,(IF DATEADD('day',-3,TODAY()) = [Date] THEN "Keep" Else "Drop" END),

    //Monday

    IIF (DATEPART('weekday',TODAY()) = 2,(IF DATEADD('day',-4,TODAY()) = [Date] THEN "Keep" Else "Drop" END),

    //All other days

    IIF (DATEADD('day',-2,TODAY()) = [Date],"Keep","Drop")))

WHEN "Past Week" THEN

    IF DATEPART('weekday',TODAY()) = 2 THEN

    (IF (DATEPART('week',[Date]) = DATEPART('week',TODAY())-1 OR (DATEPART('week',TODAY()) <= 1 AND DATEPART('week',[Date]) = 1)) AND DATEPART('weekday',[Date]) < 6 AND DATEPART('weekday',[Date]) > 1 AND [Date] > DATEADD('day',-365,TODAY()) THEN "Keep" END)

    ELSE

    IF (DATEPART('week',[Date]) = DATEPART('week',TODAY())-1 OR (DATEPART('week',TODAY()) <= 1 AND DATEPART('week',[Date]) = 1)) AND [Date] > DATEADD('day',-365,TODAY()) THEN "Keep" ELSE "Drop" END END

WHEN "Current Month" THEN

    IF DATEPART('month',TODAY()) = DATEPART('month',[Date]) and [Date] > DATEADD('day',-180,TODAY()) and [Date] <= {[Last Transmited Data]} THEN "Keep" Else "Drop" END

WHEN "Past Month" THEN

    IF (DATEPART('month',TODAY())-1 = DATEPART('month',[Date]) OR (DATEPART('month',TODAY()) = 1 AND DATEPART('month',[Date]) = 12)) and [Date] > DATEADD('day',-180,TODAY()) THEN "Keep" Else "Drop" END

WHEN "YTD" THEN

    IF DATEPART('year',[Date]) = DATEPART('year',TODAY()) AND [Date] <= {[Last Transmited Data]} THEN "Keep" Else "Drop" END

WHEN "Custom" THEN

    IIF([Date]>=[Start Date] AND [Date]<=[End Date],"Keep","Drop")

END