I understand that Yemenite congregations still use a metargem - a person who translates each Torah verse being read into Targum Onkelos. (The metargem was much more common centuries ago.)
O.C. 585:5 says that one can fulfill one of the mikrah obligations by reading together with the Torah reader during the Shabbat Torah service. (See Mishnah Berurah note #14 for dissenting opinions.)
Can the metargem ,assuming that he has already done the 2 Mikrah part (see a previous par. in the same chapter of O.C. that says that one must already complete the 2 mikrah before doing Targum.) similarly, fulfill the targum obligation at that time?