Help! Product Option Logic Isn't Logical

I have a somewhat custom product that has several options, and the logic is as such:

First, select A, B or C.

If “A” or “B,” no additional options are necessary. At this point, simply display the associated product image, add to cart and check out.

If “C,” two additional options, (for simplicity, let's call them “color” and “size”) are necessary in order to complete the purchase. As such, “A” “B” and “C,” as well as “color” and “size” are sequential options that are inventoried. But here's where I run into a big problem:

In order to complete the product, CS Cart requires option combinations that combine “A” and “B” with “color” and “size,” even though those extra options are completely irrelevant to “A” and to “B.”

What I'm looking to do is create only option combinations of color and size when “C” is selected, but this seems to be impossible.

I've been searching manuals, guides, this forum, Google, etc. for two days now and I haven't found any answer to (what I would consider) a fairly mundane piece of functionality.

Any help would be incredibly appreciated!