No. On Windows the only way to start a new executable is to create a new process (with the CreateProcess function, which all spawn* and exec* functions ultimately call), and this yields a new PID.
This is a fundamental difference with unix, where the only way to create a process is to clone the current one with fork().

And yes, this makes launchers more difficult to write on Windows.  For a discussion see the paragraph "Process Launching" in http://www.python.org/dev/peps/pep-0397/