Yes, there is a workaround if you are willing to enter measurements. Use the Rectangular Marquee Tool to make a selection - see the Options bar. Then do Image > Crop, which will delete the cropped pixels. Alternatively, the CS6 Crop Tool will be automatically snapped to a selection when activated and you can choose to hide cropped pixels if you don't want them permanently deleted.
If you are doing the same Crop, and setting the numerical dimensions, those should be "sticky," in that once added to the Crop Tool's Option parameter boxes, they should be there, the next time that you select the Crop Tool. Are those dimensions not sticking for you?
Europe, Middle East and Africa