The log is fastened to the guide board. Blocks were nailed to the log such that the front edge of the block is exactly centered with the desired cutting plane. The fence was adjusted so that the saw blade lined up also with the intended cutting plane.

Quite honestly I was worried that this jury rigged setup might jam and cause the saw to bind but it actually worked quite well.

The log is now ready for ripping. I'll rip one side and then flip it over and rip the other side always keeping the base up against the fence.