I figured out how to do it!
What you need to do is make the height of the CAPTION image the total height of the two preferred caption bar sizes, + 4 pixels (two empty rows of pixels on the top and two rows separating the two images). Then you place the top and bottom sizing margins where the empty pixels are.
So say for example you wanted the caption bar to be 22 pixels high. You would then make the CAPTION image 48 pixels high (22+22+4). Proceed and make the sizing margins x, x, 0, 22 (the x's are whatever you want them to be). The horizontal sizing margins should be in the empty space above the caption bar image.