I'm probably under thinking this, but a higher compression ratio means higher peak cylinder pressure and therefore more force against the piston. Of course, a higher compression ratio also means more energy to compress the charge. But the compression takes less energy than the piston absorbs on the power stroke, so, say, doubling both should create a net gain.
To use a very simple example, if the piston expended 1 unit of energy on the compression stroke and absorbed 2 units on the power stroke, the net gain would be 1. If you doubled the pressure so that compression took 2 units and combustion gave 4, the net gain would be 2.
Of course, reality isn't nearly that simple (for example, there would be a real pressure difference only near TDC), but I don't see why the principle wouldn't hold. Or at least I don't now -- it will probably take 5 minutes for someone to point out the fatal flaw.