I tried to do that, and following Multi-Script worked already
@var $strFile = AskText("File Name", "");
@var $strPath = "";
if ( IsTypeString($strFile) )
{
   $strPath = GetSourcePath() + $strFile;
   SaveStringToFile($strPath, "", 0);
   @var $strCmd = "C:\Program Files\Programmer's Notepad\pn.exe" < type the path of your editor instead >
   MC.Run CMD="{$strCmd}" ARG="{$strPath}"
}