Well Donald, you can do it and get the advantage of a return loop to the upper freight yard so you can have trains leaving from the east and returning from the east and not just running around in circles.
You would have to shorten the right end of the upper yard about 4 or 5 inches and run another curved track out of the main there and descending down the right side past the staging yard around the front and up to and under the center peninsula.
The track layout there would be a multi track staging yard that would turn back down and connect to the track along the front. This can be as long as your longest trains as long as you keep the grade reasonable.
This would be much easier with open bench work as the lower level staging yard would be level but from there on up everything would be track bed on risers. I prefer that anyway because the culverts and bridges over waterways , etc. are much easier if the track is already elevated. You can also do cut and fill sections easier with the roadbed on an embankment.