I've drawn up a few sketches of how I intend it to work. The general principle is that of a G1 Headmaster figure, only scaled to fit E-Scorponok, and with better articulation.
One of the sketches:

I've started with the face, which will also form Zarak's back piece.
Here's the piece so far, Blu-Tac'd onto Scorp's head. It's literally just constructed using layered pieces of sheet styrene. The brow piece, which will form the hinge that lets the crest cover the face, is a piece of small styrene tube.
