Alternative to 'setting' blueboard joins

Gday all,
I'm in the process of building my retaining wall which I will be blueboarding over and paint it using one of those render look paints.
I will be putting a 140x25 Merbau cap on top of the 800mm high wall and blueboard only on the face. I'm after peoples ideas as to cheaper/easier methods of joining blue board.
I have seen a metal strip put vertically in the join and used as a sort of feature, I had also thought of using a piece of 90mm merbau to cover the join but I think this may look ugly.

Does any of the creative thinkers here have an idea on what other option are available?

Cheers

if its a brick/ block retaining wall which im assuming it is why dont you just cement render it, cheaper and you get a better finish with no cracking !!??