But they could combine some runs. They could add a train from Greenport, have it arrive at Ronkonkoma at 7:56, and it would leave Ronkonkoma as the regular 7:57. The only difference is that now, the 7:57 from Ronkonkoma actually originates in Greenport and that it is now a C3 consist. This way, there is no addition of a train into NYP. It's still the same 7:57. The only addition is the stops between Greenport and Ronkonkoma.
Another one they could do combines a montauk and a bethpage train. Push the 5:39 from Montauk back 10 minutes. This is the train that operates via the main line and already stops at Hicksville and Mineola. Add Bay Shore as a stop. Then, combine it with the 7:58 train that originates in Bethpage. The 7:58 already goes to all the way to NYP. So now, it's all one train, from Montauk. It makes all stops to Sayville, the Bay Shore, Babylon, Bethpage, Hicksville, Mineola, Jamaica, NYP.
So there, that's 2 more trains from diesel territory into NYP without actually adding more trains to NYP. I figure both of those would be long enough to have to use 2 engines each, so that's 4 engines down, with 9 left.