Lulav And Hallel

In the past, my father discussed the opinion of the Gr"a that one can say a beracha on the lulav without turning the esrog over.  In fact, the Gr"a holds it doesn't help to turn the esrog over since the beracha is on the lulav and the law is one does not need to hold all the species together (651:12,) one has already fulfilled the taking of the lulav before the beracha.  

The Gra (646:1) says the reason the Shulchan Aruch says to take the lulav right before hallel is because the Gemarah Pesachim (117a) says אפשר ישראל נוטלין לולביהן ואין אומרים הלל.  Therefore, one should fulfill their obligation of lulav at the time of hallel.  In the Maaseh Rav with miuim in the back they want to suggest a chiddush based upon this Gra that if one did not have a lulav when saying hallel, when one obtains a lulav they should have to say hallel because lulav is its own מחייב of hallel irrespective of the hallel of the yom tov.