The ruling on the imam performing the regular voluntary prayer before Fajr when he arrives late

Your Eminence! An imam arrived late to the mosque for the Fajr prayer, and the congregation is waiting for the prayer. Is it better for him to order the iqamah (second call) to be made, or should he pray the two rak'ahs of the regular voluntary prayer first and then make the iqamah?
If it would be difficult for the ma'mum (those praying behind the imam) if he prayed the two rak'ahs, then it is better for him to lead the people in prayer and then pray the two rak'ahs afterward. And if it is not difficult—as is usually the case—then he should pray the two rak'ahs first, because when they see that he has arrived, the matter becomes easier for them.