But you can only achieve it if you spared the mages in Broken Circles in DAO, used a neutral stance the longest possible in DA2 that avoided causalities with Bethany surviving DA2 has a circle mage. Otherwise, you'll have to wipe out the mages or templars out of existence and either Vivienne or Cullen with suicide themselves.
Funnily enough that's exactly what I did. But unfortunately I doubt that would result in a compromise option. Admittedly I only know about this from other people saying it but, didn't David Gaider supposedly dislike the existence of the compromise option in ME 3?
Rannoch is super sad when choosing either the Quarians or Geth, especially if you have max relationship with both sides at the time (as in Tali and Legion are both alive and know eachother) and that sounds exactly like the thing a guy who supposedly loves fan tears might force players to confront to get what they want.
I would hope that choosing either side doesn't result in the death of all the others like it does on Rannoch though. It's possible it will I think. Even if the Inquisitor's decision doesn't kill them all in the Hinterlands or whatever, we've been told that bringing in one side to the Inquisitor will cause the other guys to become "officially the bad guys" and start causing problems in the countryside.