I made a jig to mount my circular saw on it's side so I could slide it around the piece which is held in the proper orientation to the base / work table. Keep in mind that the jig may need to have more reach for the cuts on higher up where the slope away from the bottom gets further over.
This take care of the cut coming out level ever time, whereas if you tried to cut the individual parts, even if the lines were laid out exactly right on the surface, the angle to the face is constantly changing.
I wish I had some pics of the process, but I made this long before I got a digital camera, and frankly I don't recall exactly how I mounted the hand held circular saw to the jig, but it was probably a couple of screws through the front of the sole into an angle iron, which was screwed to the arm of the jig. the arm of the jig would slide up and down a column of the jig base.
Think virtually like running ridial arm saw out to the end with the motor laid over in the yoke so the saw would be on its side. I'm not recommending that, but this is about what it amounts to. You will need a really big work-table, because my jig had a footprint at least 2' x 2', and my base was at least 3' circumstance, although yours is a bit smaller.
Otherwise, if you want a quick and dirty method that just wont cut as fast, think about using a multi-tool mounted on an arm that can move up and down,