Just a thought.
The OP talks about a lintel across the inner skin. Does this cross the cavity? I had something similar across a set of French Windows. The inner skin of the cavity had a concrete lintel which was probably cast in place. This was wide enough to cross the cavity and the height of the soldier course. The soldier course was then built directly on top of the steel Crittal windows. All fine until DG company removed the window and the soldier course (but fortunately not the brickwork above started to sag. Under these circumstances I wonder whether a piece of angle iron that was screwed to the inner lintel at regular intervals would provide sufficient support.
Andrew