Go to the image pull down menu > adjustment> levels.
At the top of the levels menu, select cyan. at the bottom you'll see fields for output levels. In the first field (The one with 0 in it) Type in the number 83. Now repeat the process for Magenta nad yellow. This should get your Rich Black to the desired percentage. You can change the number in the First output field and check the results by using the info pallette. I figured 83 would get your CMYK to the 270% you're looking for
Be careful. this will alter the color for the entire image. If you can select just the Rich black and adjust that independently.