Customize prompt lookup behavior in a dbgrid

How can I set a column in a dbGrid to ignore the prompt under certain circumstances?

1. Via customizing the prompt method in the object

 Procedure Prompt
   Integer iColumn
   Boolean bOk    
   move (true) to bOk
   Get Current_Col To iColumn
   If (iColumn=4) Begin
     // if in column 4 then check data
     Get Field_Current_Value Of Server_DD Field Foo.bar To sBar
     If (sBar="foo") Move (false) To bOk
   End
   If (bOk) Begin
     Forward Send Prompt
   End
 Procedure // Prompt

2. Via entry_display

  if(certain circumstances) begin
    Set Prompt_Button_Mode to pb_PromptOff
  end
and
  On_Key kPrompt Send myprompt

  Procedure Myprompt
    if(not((certain circumstances)) forward send prompt
  End_Procedure