To avoid cropping your image, you may be able to get away with slightly distorting the image to maintain the desired aspect ratio with an added border.

Make a new bottom layer. Fill with the border color of choice. The canvas size will be the same as the image (8 x 10 or 11 x 14)
The image layer will be on the top layer
Add guides 1/4 inch from each edge.

Free transform the image layer until it snaps to the guides. (1/4 inch in from all sides)

The slight adjustment should go unnoticed. The relative change is much less than having borders with uneven widths.
forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=38646968