You could make a pine duplicate of the wood you're imbedding and use that to displace the concrete in the mold. In the show I watched, they didn't mold it upside down, they poured a very liquid concrete into the a mold, then let it settle undisturbed. If I did this, I'd put some stainless steel mesh in the mold. Remembering the TV show, I don't recall they put in any kind of reinforcement, it was poured over a plywood base as a kitchen counter top. Seems to me it would be a little fraile on the edges and sure to chip at some point. And any air bubbles would be very bad news (weak spot).
The more I do, the less I accomplish.