with no real answer. The dumb answer is simply that it was never done by the DL&W. The execptions cited (two trains out of Dover around 7am back in the late 60s or early 70s "hop schotching" to Summit) did not last long reportedly because some crews could not keep straight what stops were to be made while another report was that commuters couldn't keep straight which was which; in either case some dangerous situations supposedly developed. In reality, I don't believe anything was gained, time wise or service wise, as the second train was always on the first's markers. So in practicality today, either eastbound or westbound, the congestion generated would negate the the value of expressing.
But further, I believe NJT should rethink its engine and car trains in favor of more MU equipment. While the versitility of engine and car has a factor of being able to exchange equipment across lines for economic reasons, the faster starting and stopping of the MU type train provides faster schedules and more traffic capacity on a given track at a give time. Such a move would eliminate the need for express service west of Summit.