I cut this 2ish x 7.5 inch x 2 ft piece of walnut by hand. I know that you're going to be sawing a lot more than this, but it can be done.

I marked two lines around the whole board referencing the same side, with the two lines being my max kerf width. I clamped the board at an angle and established a good kerf down each side of the board. I then vlamped the board straight up and down and sawed straight. It took a while, but I had no other option for cutting this board. I've been seriously thinking about building a big frame saw, but havent gotten to it yet.