Without a photo or diagram, it's hard to say. But I'll just mention that I have seen some engine controls rigged with both a fuel shutoff and an emergency air-intake closure, to starve the engine of oxygen. Another possibility is that you are looking at a remote compression release.
Just my WAGs...
P.S. That's looks to be a lot of boat for the money!
Good Ideas Thanks.
Yes we liked it a lot too.