#define ForeignSetup "ForeignSetup.exe"

[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Files]
Source: "{#ForeignSetup}"; Flags: dontcopy

[Run]
Filename: "{tmp}\{#ForeignSetup}"

[Code]
const
  ForeignSetup = '{#ForeignSetup}';

procedure InitializeWizard;
begin
  MsgBox(ForeignSetup, mbInformation, MB_OK);
end;