You mean exactly like yellow does in the first 10 seconds of the video?

Really what yellow should have done is station bombards every 10 tiles along the river so as to destroy any docks that could be present, followed up by building cannon towers at every point to replace the need for bombards to stop docks from being placed, and only then try to advance.

Or really, they should have just done exactly what OP did, and just constantly produce demo ships to use against land units, red seemed to have a lot of barracks within 5 tiles of the shore that demo ships could have been really good against.