sealing window reveal where house is stone faced

the construction of our outer wall is 8inch stone, outer leaf block, cavity with 60ml insulation, inner leaf block. because of the stone facing the windows are sitting on the outer leaf block, whereas normally they would be on the cavity, hence there would be no break in the ring of insulation. Now the insulation is finishing in the window reveal, so how do we finish this efficiently so as there is no cold bridging? thanks