No, he couldn’t. He had already tried everything. He said not to worship him, more than once. Malcador said not to. Other Primarchs had told Lorgar he should cut that shit out, both his friends and enemies among his siblings. Finally the Emperor has to come all the way to Lorgar’s latest project, Monarchia, and he brings Guilliman with him just in case he has to use him.
They evacuate all Monarchia, and the Emperor asks, again, to stop it. Lorgar still says no, and starts screeching about the Emperor will surely accept that he is a god once he sees what Lorgar has built for his God-Emperor. And then he is told, again, to cut that shit out. And Lorgar loses his temper so hard he decks Malcador, punching him dozens of meters. The Emperor’s arguably closest confidant, and genuine friend. Had Malcador not been a Perpetual and powerful psyker? Or an ordinary human, or even an Astartes? He would be fucking dead.
So the Emperor has tried every possible carrot. He resorts to the stick and has an empty city razed. Because there was no other way to get it through Lorgar’s retard skull.
Emps’ only mistake was in not offing Lorgar then and there. It would have been a mercy kill.