You can't put the two pumps in series, but you could put them in parallel so either could operate. If you go to the trouble of adding an electric pump, just bypass the engine driven one and use the electric all the time. Any fuel pump suitable for diesel should be fine. Go with a low capacity as the 5411 is only 11 HP.
Not sure why you seem to be needing to bleed the fuel system so often. Only had to bleed my 5411 once in 20 years.