How to hook a method to the Edit event in Delphi 7 IDE?

I'd like to automatically checkout a file when I start to edit it in Delphi 7 IDE.

ClearCase is my version control system and I really hate the need to checkout a file before starting to edit. It always breaks my thought flow: I'm trying to solve a problem, find where I need to change, try to edit it, fail because the file is read only, open clearcase, search the file, finally checkout, try to edit the file again, fail because the IDE still thinks it is readonly, tell the IDE that isn't readonly. When I finally go back to code, I forgot what I was trying do do.

I've found this nice and simple ClearCase IDE integration code. It works, but uses the deprecated ToolIntf unit. I've added a couple of shortcuts. Here is a simplified version of it (didn't try to compile):

unit clearcase;

interface
uses ToolsApi, ToolIntf;

implementation
uses
  Windows, Dialogs, Classes, ExptIntf, Menus, ShellApi, SysUtils;

type
  TDelphiClearcase = class
  private
    FClearcaseMenu,
    FDoCheckOutPasDfm,
    FDoCheckInPasDfm : TIMenuItemIntf;

    procedure ExecCommand(const command: string; path: PChar = nil);
  public
    destructor Destroy;override;
    procedure DoClick(Sender: TIMenuItemIntf);
    property ClearcaseMenu: TIMenuItemIntf read FClearcaseMenu write FClearcaseMenu;
    property DoCheckOutPasDfm:TIMenuItemIntf write FDoCheckOutPasDfm;
    property DoCheckInPasDfm: TIMenuItemIntf write FDoCheckInPasDfm;
  end;

var
  dcc: TDelphiClearcase = nil;

{ TDelphiClearcase }

destructor TDelphiClearcase.Destroy;
  procedure Remove(item: TIMenuItemIntf);
  begin
    if( item = nil )then
      Exit;
    item.DestroyMenuItem;
    FreeAndNil(item);
  end;
begin
  Remove(FDoCheckOutPasDfm);
  Remove(FDoCheckInPasDfm);
  inherited;
end;

procedure TDelphiClearcase.DoClick(Sender: TIMenuItemIntf);
  function GetPasDfm(const f: string): string;
  var
    aux: